hi if it were me i would get at least 2 of every species as i think fish like to have at least one friend of there own kind, imo anyway, happy fish shoppping! x
I don't think you've quite understood this, Bex.
Some fish are schooling fish and need to be in groups of at least 6-8. Glass catfish, in particular, have been known to pine away and die if kept singly or in pairs. Danios for instance often get aggressive if kept in pairs and may end up killing each others.
Other fish are so territorial that you can only ever keep one in the same tank.
And some fish are in-between.
Of the ones on your list, clay roper, I would say your suggested number for neons is very good; you would need more glass catfish (6-8) or none at all; khuulie loaches also will be a lot happier if you keep at least 4-5; bristlenoses don't mind so much, but you are better off not getting more than one male (the ones with the bristles), though you can get a pair; I would not keep more than 1 gourami, unless you are going for a pair or better still a trio of 1 m, 2 females.
Other factors to consider: none of those fish are hardy enough to cycle a tank so you will need to read the topic on the fishless cycle and start looking for liquid ammonia.
Also, some fish are so sensitive that they should only be kept in a mature tank (one that has been up and running with fish without problems for several months). This includes the neons, the dwarf gourami (if you go for that) and the glass catfish.
So, you will want to first do a fishless cycle, then add your hardier fish: the bristlenoses and khuulies and if you decide on the opaline gouramis. Then after a few months gradually add the neons, then the glass cats.
Now for the maths- and this is going to be my downfall! Assuming a trio of opaline gouramis, 10 neons, 2 bristlenoses, 6 glass catfish, 5 khuulie loaches, I should say a 240 ltr tank (63 US gallons) should do you. I've just been out to look at a tank that size myself, and you can do a lot with that. If you go for dwarf gouramis you may be able to get away with a 55 gallons (210 ltrs) but I wouldn't go much smaller than that. You will need to provide hiding places for the khuulies- funnily enough they show themselves more the more shelter they have; bogwood for the bristlies; a sheltered area for the glass catfish to stand. Gentle water movement and plants will be good.