Lol! All I can suggest is - work with what you have got and make another enclosure and then see what it might be suitable for? It's great to be all enthusiastic and very creative
But I find sometimes you end up, as you say, getting too much confusion and chaos and then either finding you've bitten off more than you can chew, or you then need to buy even more materials to get it right.
Sorry that probably isn't much help. Because I guess you need to know what pet is in mind to know how to build it.
I'd suggest just taking deep breaths and one step at a time, and one pet at a time, so you have enough personal reserves to give each one the attention needed, especially in the first few weeks
Ferret enclosure sounds overwhelming to me. Rats are better with cages. Guinea pig enclosure sounds good
The grids could be used to make a playpen? Kitten sounds good if you can keep your hammy and guinea pig in a separate room the cat can't get in.
So I would go with - existing hammy, guinea pig enclosure. Keep the grids for some sort of playpen. Burmese kitten. A friend of mine had Burmese and they're almost like dogs they are so clever and interactive. Cats can look after themselves quite well. Guinea pigs and hamsters need a lot of human attention. So maybe start there and see how it goes
Rome wasn't built in a day .....
Ultimately it sounds like you need a pet rescue or pet shop!