I think 1 is the perfect amount. I don't really know Dark Angels that well, but let's be real here. If you're spending $120 (less in your case), one will probably do! It will look great on the table, be lots of fun (hopefully) and not be tremendously overpowered nor hindering. I'd go for it if you have the cash.
Secretly, I'm still planning a Chaos conversion. I dare my friends to tell me I can't use it... (*hopes his bluffs work on someone*)...
Friends are supposed to be enablers, not limiters. If your friends tell you that you can't do something, they aren't really your friends.