What To Do With 2nd Tank

Before we advise on suitable fish, can I just check that your water hardness is 7.14 degrees Clark and 102 mg CaCO/litre? I found this in a previous post but just wanted to check that this is definitely the water hardness for the place you're moving to?

I would go with sand in both tanks simply because it gives more options than if you were to use gravel. I can't think of any fish suitable for your sized tanks that would benefit from gravel over sand.

Will you want to get of the same fish again or would you prefer to get all different? And can you remind us how big the current (empty) tank is?

I would be very tempted to make the two tanks different from each other in some way. Or to do a biotope type setup in one. 

A biotope is where all the fish, plants substrate and decor all come from one place in the world and the aim is to recreate that environment as closely as possible.  They can be a real challenge to get right when you are researching them and setting them up but they are not neccessarily a hard style of tank to keep.

Another thought... You can put additives in your water to make it harder if you want to be able to stock fish that you otherwise wouldn't be able to.  That might be an easy way of making one tank different to the other.

I now have a community tank and a dwarf puffer tank for example. Fish that could never be housed together in the same tank. The plants are all different.  The hardscape materials are the same, but the layout very different.

I would recommend setting up both tanks to be relatively low maintenance so as to avoid creating a problem for yourself later down the line.

I would be very tempted to make the two tanks different from each other in some way. Or to do a biotope type setup in one. 

A biotope is where all the fish, plants substrate and decor all come from one place in the world and the aim is to recreate that environment as closely as possible.  They can be a real challenge to get right when you are researching them and setting them up but they are not neccessarily a hard style of tank to keep.

Another thought... You can put additives in your water to make it harder if you want to be able to stock fish that you otherwise wouldn't be able to.  That might be an easy way of making one tank different to the other.

I now have a community tank and a dwarf puffer tank for example. Fish that could never be housed together in the same tank. The plants are all different.  The hardscape materials are the same, but the layout very different.

I would recommend setting up both tanks to be relatively low maintenance so as to avoid creating a problem for yourself later down the line.

Both ideas are interesting but not sure how I would make my water harder. How would I do that?

It may also make this slightly more difficult when acclimatising new fish, as the shop will most likely have used local water.
You'd be amazed at how many fish you can keep in your water, so it may not be necessary to harden it.
Have a look around your LFS first, see if anything takes your fancy. 

Had a look around at the LFS and seen some fish I have never seen before, but need to make a return visit. In one shop there was a fish names mickey mouse or Minnie mouse, or something very similar. Was thinking of Barbs in one tank as I know they are not a big community fish.

Mickey mouse platy? They are quite colourful.
You may have to harden you water a bit for them.

The more I read about tetras I definitely want some of them. The penguin and lemon tetras look great.

I have both and I think they are lovely.
I have lemon tetras in a Fluval Roma 125 (80cm). They are with a BN, some glass blood bloodfins and gold stripe corydoras. The colours/marking on the lemon tetras are lovely.
I have penguin tetras in a 125 with some hatchets, a BN, and black neon tetras. I like the way that penguin tetras hang around slightly nose down, and they are quite active fish.

Yes, I have tanks where the fish are slightly colour co-ordinated; the first tank the fish all have yellow/orange/red colours, and the second tank the fish are all dark/black/silver. 

What is a BN?

Sorry.
I have Bertie, who is a yellow male, and Harri, who is a standard female.
They had to be put into separate tanks after the egg laying/hatching incident last year - they were at it roughly every 4 weeks, it was crazy.
I think Bertie has some lovely bristles and is a very nice chap. I also like watching him feed on the front glass as the way his mouth moves reminds me of a sock puppet.