The "I won't get them all line", yeah I said that too. 5 SBRs ago. Now I just need a MP5SD, and maybe a MP5K......
On the cans, unless you just want to buy several, get bigger than you need. If you need a 9mm, get a .45, if you need a 5.56, get a .308.
That Coharie has been on Gun Broker forever. Use caution.
Funny you say that, since I just got an MP5SD and an MP5K (well, a Coharie variant of both), which more or less "completes" my HK sear host collection, minus a few odds and ends like an HK21/23, HK11/13, and an HK51 SBR.
Since I now own a grand total of 5 Coharie/Special Weapons roller locks and one of their HK416 clone uppers, I will say you should go into buying any of their guns assuming you'll have to do some work. Now, the work might be minimal, but assume you'll have to do something to them. Use that assumption to help factor the price you are willing to pay, when comparing it to the other HK options (like an MKE or POF recent build, or a very pricey build from some of the other clone builders, but those are all going to be north of $2k).