Should I buy a bigger tank? Already?

I'd buy a 1000g tank if it would fit in my house right now...lol BIGGER RULES

 

I would say go as big as you can but also do a ton of reading about other peoples builds and how to do the filtration system so hopefully you minimize those "I should have done it differently" type of regrets.
As someone else mentioned you can use the 25 as a sump for your new setup.
It also depends on what you want to stock and if you can comfortably afford the stuff needed to get the larger system operational, keeping in mind also that whatever system you get you'll have to move it eventually when you move out and every time you move, but a 65 shouldn't be that bad to have to move.

 

Ideally I want as big as I can have. Personally, I'd like to own a seaquarium of say maybe, 20,000 gallons, But that never gonna happen lol. I went form a 27 straight up to a 125. Upgrading to a 450 when I move out.
Go for it

 

Welcome to the club..... we always want bigger and better