i encourage any new fish hobbist. it is fun and exciting. there is nothing wrong with a small tank. it can be a good educational start. just take it slow and really be certain what you would like to have in there because the space is limited. as for the platys, i would not put them in a small tank. they are messy and can be a little nippy with smaller fish. as for the cherry barbs, i have 8 of them in one of my 55 gal. tanks and they all swim together. quite nice, and very colorful. but i must say, if you added the cherry barbs,other than a couple of corys that's all i would add. you have to be careful in a small environment. small impacts can make big problems. i find it easier to maintain my big tanks than the 10 gal. good luck. 
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and it you like me have fish that are seen as scaleless or some other such oddity then you really do need to know this bit of fact PDQ!!
you like me are in love with your tank and desperate to see it set up, others in this forum are also saying they would love you to have a great set up, but just take care of your tank now and the fish you get in the future will live longer and be happier!