I do love having a Vs-forum to move these questions to.
A really good tank is an investment. I've kept the same carbon fiber tank through... no fewer than nine guns in the last five years. If you've got the money to spring for a good tank, and plan to play long-term, it's worth the money. Now, that's assuming you can get 4500 fills where you are, or where you'd play. Some fields can only fill to 3000, so that's something to bear in mind.
Hoppers are likewise something of an investment. You can pick up "more hopper" than what you need right now, knowing you can use the same hopper on whatever gun you'd pick up. I've always been a fan of the Empire loader lineup - I trust their R&D guy.
The good news here is that hoppers are pretty tough unless totally abused, and you can find some interesting deals right here in the BST section.