ITA.
first and foremost, you need to make sure the bag works for you and your lifestyle, so you'll actually use it. are you hard on your bags or do you baby them? do you prefer hobos, crossbody, satchels, etc? do you carry a lot of stuff or do you carry just the essentials? if you don't use the bag, what's the point?
you should really love the bag before you buy it. like others have mentioned, don't settle just because one color or texture was a better deal. you'll end up spending more money placating yourself vs just buying the bag you really wanted to begin with.
sleep on it (for a night or two or three). sometimes just giving it some time helps you determine whether you REALLY love the bag or not.
try to see the bag in person first before buying. go to a store or find someone you know who has one, etc. sometimes that will tell you instantly whether or not the bag will work for you.
if you end up not loving something, give it up and pass it on to it's next owner, who will hopefully be happy with it. no sense in keeping something you don't like or use.
moderation is key. are you someone who changes bags frequently? or do you use the same one for months on end? will you really use the bag or do you want it just to have it?
as for the money piece, i won't tell you how to manage your own finances. i wouldn't recommend spending above your means, but that's just my opinion.
and like everyone else has mentioned, tPF can be addictive and really hard on your wallet, since you'll see so many things you like, but don't necessarily need or love. i don't regret finding tPF, but i don't think i ever would have had a designer bag "collection" if i didn't.