Hey Pit,
I happened across this, so hope you don't mind me sticking my 5p worth in!
I'm quite new to all-grain brewing and new to this site, but you seem in two minds so thought some advice might help. I was pondering for ages what kit I'd need, how much room I'd need, etc. and was in danger of spending loads of dough...
I finally decided that rather and go the whole-hog first time round, I'd try BIAB. I bought a 20l pot (no tap), a mash/sparge bag, and an all-in-one all-grain kit (grain/hops/yeast). It makes things dead easy. Heat up the water, stick in your grain, let it soak. Take the grain out and sparge by rinsing or dunking the bag, then boil what you have left, adding your hops as you go. Cool it down, chuck it in the fermenting vessel and chuck in your yeast. It really is that easy. The pot and bag cost me £40, and I assume even if I upgrade a 20l pot will be of some use (and if not, I've not lost much).
You'll need an FV (with bung/airlock possibly) sanitiser, bottles, caps, capper and a syphon but other than the bottles, that's all pretty cheap, and will all be reused, other than the caps. Of course, there are lots of other things you CAN buy, but honestly the above will get you drinkable beer in a few weeks, and is an easy win...
It means the entry into AG brewing is quick and easy, and means you haven't bought loads of kit you don't need/won't use.
It's also nice that in the 20l pot with a 15l recipe I end up with maybe 20 or so bottles of beer, so I can try lots of styles/flavours/recipes (I have about 40 - 50 bottles lying about, you can often pick these up for free or re-use beer bottles you drink from if they happen to be brown..).
Anyway, just thought I'd pipe up - don't want to put you of your purhcase, but just showing that getting into it for the first time can be cheap and easy... Others may disagree with my line of thinking, just thought I'd share my experience!
Cheers.