I personally think you will be fine adding more, and I would agree with going with at least 2. First, since silkies are bantams they tend to not need as much space. You are on the right track with leaving the new guys separate until they are big enough to defend themselves. The best way to introduce them would be to have the new guys out with the original group where they can see them but not get to them. Maybe section of part of the coop/run for them for a week or so. They will get use to seeing them there. Once they seem disinterested, you can add the new guys at night. From everything I've read, they do best when introduced at night and wake up with each other.
We have chicks in a grow out pen connected to the coop/run of the big girls. After a couple of days they don't even care about the other guys. A couple of curious chicks pushed under the wire and got in with the older girls, they are a year old, and for the most part they ignore them. There was a little blood on the chicks from scratching themselves going under the wire and even that didn't cause a frenzy. We do have a head hen that is pretty much a bully, when we introduce the new guys for a permanent stay, we will remove her for a couple of days so the other girls don't pick up on her bullying. Ours will be able to free range together a few times before we introduce them in confinement. We've added our 2 bantams in with the group of chicks and they could have cared less, until they realized they weren't able to free range with the other girls and then they wanted out.
Everyone has different experiences.