98L [orig Intended 54L/12Gal Tank] Stocking And Filtration Ideas?

From what I've seen of on-line shops, they don't let you select the sex of fish, but you can always ask.

I'm quite surprised that none of your local shops stock rams. Do they not have rams of any type? Any rams other than bolivian rams are all the same species, Mikrogeophagus ramirezi (bolivians are M. altispinosus)

If you like Lampeyes check out some of the 'Blue eye' family (Pseudomugil). They also have the blue eyes and are a similar size but are much more flamboyant and colourful.

The males are the ones with the long fins. The females look like lampeyes with slightly coloured bodies, still attractive but not a patch on the males. I'd recommend 2m 4f for a group of 6. Whilst this may not sound great, you'll actually see a lot more of the males finnage as they display for the females. The males do spar from time to time, but most of their flaring is for the females. Personally rather than having 4 CPDs and 6 Blue Eyes, I'd go for 10 of one variety. They're much happier and more impressive in larger shoals.

I don't think you'll have any problems with fin nipping. Neons aren't particularly nippy, especially in a decent sized shoal. I keep 4 Xray tetras with my Pseudomugil and have no problems.

I have 7m and 2f in my tank as they were all the Pseumugil sp. red neon I could find at my 5 closest LFS. I wish I'd got 3m and 6f as most of the males don't flare, only the 2 or 3 dominant ones do. I'm pretty sure that a 2:1 female to male ratio would have resulted in much more displaying as the males compete for the female attention. You're also more likely to get successful spawning with that ratio.

They're boisterous little blighters but don't think all males would be a serious problem.

A male and female that don't like each other could end up fighting.
With fish like rams the usual advice is to get several juveniles, wait till a pair forms then return the rest to the shop. The problem with this is that not all shops will take the 'spare' fish back.

Two females should co-exist with no problems.

Do you have a Maidenhead Aquatics near you? They usually have them in stock.

Over the years I've had bolivian rams and apistogrammas spawn in a community tank. The bolivian rams laid eggs on a flat stone (I think non-bolivian rams do this too) while apistos spawn in a cave. The parents of both types chased other fish away, but only a short distance and only as a warning. Once the intruder was far enough away, the parents no longer chased, and even when they did, they didn't make contact. Because the eggs and newly hatched fry were safe in a cave, the apistos managed to raise their fry to the free swimming stage, when they were promptly eaten by their tank mates. The bolivian rams didn't get that far. Because the eggs were out in the open they were eaten pretty quickly. If there are more than two other fish in the tank, while the parents are chasing two fish, numbers 3, 4, 5 etc sneak in and grab an egg or two before the parents get back.

So, in summary, no fry survived into the free swimming stage in a community tank and although the parents of these two types chased the other fish they did no harm.

Disclaimer - there are always exceptions to any rule! And cichlids other than bolivian rams and apistos might be nastier to tank mates.

Can't comment on the Rams as I've never kept them. I've heard they are sensitive fish so don't be too hard on yourself if you lose a couple.

With regards to stocking, whilst you don't have any fish that are known for being particularly tough, provided you've cycled the tank correctly most should be okay with two exceptions: Otos and Shrimp. They are algae eaters that require a mature tank. leave the tank a good few months before adding them. I'd say the Rams would also benefit from a more settled tank. 

Just flicking through the latest PFK and it says that Blue Rams are captive bred and consequently more resilient than their wild caught cousins. Might be worth trying to track some down if you were going down that route over the Bolivian option.

Happen to be reading the PFK at the moment so, to answer that last question, it says "Blue ram - Mikrogeophagus ramirezi" and refers to them as being "farmed, non-naturally occurring fish with a greater tolerance of water chemistry than wild types".

[Classifications are confusing - in the same edition of PFK, albeit in a reader interview, corydoras habrosus is also referred to as a pygmy cory. I thought corydoras pygmaeus were the pygmy cories, and corydoras habrosus were the salt and pepper cories. However, on checking Seriously Fish, it seems that the habrosus/salt & peppers can also be known as pygmies.]