I'd go for it if I were you. If the price is even a bit cheaper than buying new where you live, you'll be kicking yourself if you get into this hobby and let it go. I like the 5 US gallon size - still really easy to move around and lift at my age, plus it fits 20L standard grape juice pails perfectly after primary fermentation without topping up.
5 gallons is about 25 750ml bottles. Between myself and my wife, family, and friends, we go through at least an average of one bottle a day. Considering the wine stays in the carboy for at least 3 months before bottling, I need a number of carboys just to start a new batch or two each month and break even. So I'll have 6 to 8 carboys going at once, while 1 or 2 primaries are going.
It sounds like a lot, but you'll find out it isn't. This is especially true if you'll have friends over regularly that like your wine. You need to make an excess at first just so you can stash some away to enjoy aged a couple years.
My point is that if you get into this, even 2 or 4 carboys won't be enough.