I received some negative feedback on my other Pikachu, and rightly so, it was awful. I made it very quicky and it was not intended to be printed very large.
This one is! Print whatever size you like, life size if you're printer is big enough (mine was if you look at the photos...)
The base is optional, the tail is a reasonably snug fit BUT I do warn you, if you do it hollow and you make the tail heavy, it will fall backward, so if you do make it hollow, I suggest dropping some old coins or something in the feet when it's printing so it has some weight and counter balances the tail - I forewarned you! :)
up to you
If you print life size then you need supports under pikachu. Arms and everything else are ok, but the bridge is very large and sharp, so I suggest supports under his arse as you see in the photo yellow being printed.