New Tank Suggestions?

Before answering your questions, I need to advise you to ignore the shops. Most of them don't have a clue about setting tanks up properly. And without intending any disrespect, ignore your father too. Fishkeeping knowledge has moved on enormously in the last couple of decades.

Firstly, you say you let the tank cycle for a week. I assume you mean you let the tank run but didn't add anything? In which case, it was not cycled and you are now doing a fish-in cycle.
You say you have been monitoring the water closely - have you been measuring the ammonia and nitrite levels? If you have, good  And have you had any reading above zero for either of them - and doing water changes as and when necessary to keep them both below 0.25?

Q1.
You can add more fish when both ammonia and nitrite stay at zero without you needing to do water changes. There is no set time, it depends how long the filter bacteria take to grow. Once you've had double zeros for a week, you can get more fish - around a third of the fish in there now. If you get too many at once, the bacteria you have grown will be overwhelmed. Since you have 3 danios and 3 mollies and you want more danios, given that mollies (even baby ones) are bigger than danios, you can get 3 more danios.

Q2.
Do you want a fish that feeds off the bottom or a fish that eats algae? If it's just fish that live on the bottom, why not look at corydoras? A tank with a footprint the size of yours will need one of the dwarf species of cory rather than one of the larger species - that's pygmy cories, salt & pepper cories (not peppered, cories they get too big) and hastatus cories. They need to be in a shoal of at least 6 of the same species. They are not vegetarians despite being a type of catfish; they need to be fed on sinking pellets that contains some meaty ingredients.
If you want something that eats algae, the best creature for that is nerite snails.

Q3.
Weekly water changes of 25 to 30% is the best regime. But that's only once the tank is cycled - once both ammonia and nitrite stay at zero by themselves. Until then, water changes should be as often and as big as necessary to prevent either going over 0.25.

Q4.
With just 24 inches length, you can't have very big fish. They need more swimming room than you have.

Do you know how hard your water is? A rough guideline is if your kettle or shower head fur up, you have hard water. Your water company should have the hardness somewhere on its website. If you find it, can you give us the number and also which units they use. There are several of them (like inches and cm for length).

It is easier to suggest fish once we know what your water is like. Hardness is more important than pH. You have some time yet before getting all your fish 

Hi & Welcome Winterdusk

Just a thought about the otocinclus suggestion...they are lovely little fish, and Andrea is right about needing a shoal but I think 6 is a better number. However, that brings us to another  glitch. Have I understood your post correctly that your tank is only a month or so old? Otos really need a tank that is mature, that is a tank that has been cycled and then is 6 months or more old. It takes a while to grow a decent amount of algae for the little fellas too. They can be delicate little chaps to start with and we can give you some pointers to maximise your success with them before you buy any...if you decide on them when your tank is ready
In the meanwhile, you are going to be busy doing loads of water changes. Have a look at Sue's thread on 'Fish-in Cycling'....she tells you EVERYTHING you need to know to get a happy tank!
Good luck

Replying to this two months later because I didn't want you guys to think I didn't appreciate your replies/knowledge. I just ran into a few missteps along the way, and felt it was best to wait until I was officially on track before coming back here. Save myself some embarrassment.   

To summarize everything that happened after my last post:

I lost a few of my mollies presumably because I was not monitoring the nitrates/nitrites levels. I had been monitoring the ammonia, but had not been educated to the fact that just because the ammonia levels go down, does not mean that the tank is cycled. After that, I felt bad, and really waited carefully and did all the tests / water changes until the nitrites spiked and went down, until I was left with just a small amount of nitrates. I had one molly survive the process. She's a fighter. My danio's survived also, unsurprisingly. I didn't add any more fish until recently. Wanted to make sure everything was stable. I noticed some algae starting to grow on the inside of the glass, which I cleaned, which I take it is a good sign.

My new additions are two sunset platies and a paradise gourami who I believe is female. She's still tiny, so I'm looking forward to watching her grow.

Not sure about my water company, but the info from my test strips say that general hardness is 60 ppm and carbonate hardness 240 ppm. pH is 7.0.

I really like the salt&peper corydoras. I think I'd go for something darker because my tank's substrate and most of my fake plants are light and I need the contrast. I also like the suggestion of the Otocinclus Catfish, but maybe I'll wait a bit longer for my tank to mature before purchasing a few.. There has been some algae in my tank, but probably not enough yet.

Is there a link somewhere that would help to decide which fish I could later add with this group, and how many my tank can hold?

Thank you all to your suggestions and tips. Maybe I'll take some pics of my tank later on and post them. 

First of all your hardness - test strips are not terribly accurate. The results you give mean you have soft water (GH) but high buffering capacity (KH). Levels so different are quite unusual. If those are anywhere near accurate, mollies will not be happy in your water as they need hard water. I would confirm your test results with your water company, by phone if necessary. Few water companies give the KH on their website and if they do they call it alkalinity. If you do ring them up, ask for the hardness and alkalinity and ask them which units they use as some companies use mg CaO per litre which is not the same as ppm on our testers which is mg CaCO₃ per litre - fish profiles on all websites use either ppm of CaCO₃ or german deg so you have to convert the CaO measurement to get a meaningful number.

Paradise fish and salt&pepper cories prefer slightly lower temps than most tropical fish; the lower 20s rather than the mid 20s. You might find it tricky finding those particular cories. I have given up and got more pygmy cories. One shop I asked at said they order salt&pepper and hastatus every week but never get them. The only dwarf cories that ever arrive from the order are pygmies. With the footprint of your tank, don't be tempted with one of the larger species; I wouldn't even put panda cories on that sized footprint.

Watch the paradise fish as she grows. Males are known to be aggressive and some females are almost as bad. It is possible you have a male if the fish is very small; fry always look female until male hormones kick in at puberty. If your fish hasn't reached puberty yet, it could turn out to be a male.

As Resa says, look at the community creator on here. It is right at the bottom of every fish profile. If you want to save the info you need to log in separately from the forum. And it has a nasty habit of logging you out while you are researching a fish you want to add so you have to log back in all the time.