Welcome to the slippery slope of Amiga hardware upgrades! Once you start going down the path, you'll find it's hard to stop the upgrade fever!
I'd say start off by spending as little money as possible and see if you are still interested after a month or two. Upgrading Amigas can be very expensive because of the marketplace that exists. Figure out what it is you like to use your Amiga for (games, programming, etc) and then do the research on the hardware you want before you buy anything. Each system has its pros and cons. The 1200 seems to be the sweet spot for upgrades as there are still a lot of products being made for it. Spend a little time reading through the forums and figuring out all the technologies before you make your decision.
And also realize that lots of people come and go. I see people selling off their systems on one day and the next day somebody new comes back into the picture wanting to buy. So it's a nice ecosystem we have here.
