I think you first need to decide if you will start with the canon/pretty-sure-it's-canon stories or non-canon stories. Because some comics don't seem to be a part of the "official" story, they're more alternative dimension/what if stories. For example almost everything in Omnibus 1.
I would recommend reading the canon or maybe-canon stuff first to catch up and be able to talk about the comics as they are published(they are being published right now) with the rest of us. Deciding if you will go digital or not might be an issue, since there's a lot of comics to buy. I'm trying to get rid of my physical comics right now to buy them digitally instead, and that's a pain in the butt.
I have a recommended reading list for you. The comics within [] are maybe-canon or not absolutely necassary to follow the "main" stories. I recommend to read them, but it depends on how much you wanna spend.
[Darkhorse: Tales of the slayer/vampires]
[IDW: Spike: Asylum]
[IDW: Spike: Shadow Puppets]
IDW: Angel After the fall
[IDW: Spike After the fall]
[IDW: The 8 issue Spike series(that doesn't have a proper name for the entire series)]
Darkhorse: Buffy Season 8(includes one shots)
Darkhorse: Buffy Season 9
Darkhorse: Angel & Faith
Darkhorse: Buffy season 9 mini series(right now only #1 of the Spike series is out)
These are all collected in different ways, ask us if you want suggestions on what collection to buy. For example, if you want the Tales stories, buy the Tales hardcover to get them all.
I think, if I haven't forgotten one, those are the ones you should read to get a hang of the official stories. What's canon or not can be a hard nut to crack, but for me, it's good to know what the writes do or don't consider "real", so that they and we know what events and personal development the characters have actually gone through.
Btw, I really recommend that you one day read all comics. Some of the non-canon ones are really great.