Battle every trainer and Trade with Pokemon colleseum
No.
every where
There is no time in FireRed.
Route 225 is not a route that can be found in Pokemon Firered, route 225 is in Pokemon Diamond, Pearl, and Platinum. To get there is Diamond Pearl and Platinum, you have to see every Pokemon in Sinnoh, then talk to Prof. Rowan and get the national dex.
No you don't have to. But if you want every Pokemon you must.
you can get every pokemon using codes you can get legendary pokemon such as mew regi's HO-OH Lugia every kind of pokemon
get every Pokemon in the game then go to mystery cave and catch it
the hospitals are Pokemon centers there the red buildings in every town
Seafoam Islands.
Walk around. That's how it is in every Pokemon game. How could you not know that?
Nothing Happens
Pretty much every cave.