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>what Pokemon do you think you'd be able to have by your side?
Anything. Whatch the anime. Big ones go inside the pokéballs when you get inside buildings and the rest can go with you.
>How many do you think you could keep on hand at once?
There's no limit, from what we know. One might be enforced on you if you are a registered trainer with a pokédex, but otherwise you seem to be able to just buy pokéballs and capture whatever you want. The only problem would be to remember which pokémon is in what ball. The manga solves this problem because it lets you look inside, so that could be a thing.
>What would be your number 1.
Growlithe. I'd also have a Gengar to protect the house, Rapidash for transport, Pigeot for flight transport, Machamp for training and heavy stuff, Bulbasaur to hang around the garden and help there, Gardevoir or Tsareena for household chores, since they're the most human like and can handle things like humans. If I found one, a Shaymin too, just because he a cute boi.