You can find 556's for much less than $1600-$1800 ... I've seen them lightly used for around $1000. I have a 556 Commando that I love, it's been 100% reliable with no issues what so ever. I don't see any problems with having one as your only 'tactical' rifle, it will certainly fill that role. Personally if I could only have one rifle it wouldn't be a 223, it'd be a 308. Although that role could also be filled just fine by your Bulgy AK ... I just shot a Rifleman score with a Bulgy AK (with Tech Sights) at an Appleseed event. They can shoot just fine, and if you want to attach stuff, the Midwest Industries rail is a nice piece for a good price.
I wouldn't ditch all your handguns though, of those you list I'd keep the HiPower. If your Rock Island 1911 is 100% reliable, that would be a good one to hang onto as well. If you do sell all your pistols, replace them with at least one other pistol. A 100% reliable 1911 or a Sig 220 would be my choices.