We tend to spend most of our summer vacaion rafted to as few as one or as many as 8 other boats. Never had any difficulty, as every member of the raft has/uses their own fenders, placed where they will do some good, their own lines, also placed appropriately.
On thier first raftup, newbies sometimes need a little nudge to get things right.
For example, lots of folks have a tendency to leave their fenders at "dock height" which is too low for rafting. The fenders need to be at the height of the most likely contact between the boats, should there be a Bayliner going past. If that means buying larger diameter "Scotchman" style fenders in order to get the margin of safety needed, that is what most of us do.
Also, tying the lines so that gates will line up, or at least so the boats will stay put in their positions, sometimes requires a little nudge.
The most difficult boats to raft to are those without a side deck just where you need to board them, so we try to keep those boats to the ends of the raft, to minimuze the need to cross over.
Some rafting locations can present other challenges, like cross currents. These are common in the Desolation Sound area we frequent, but with experience, are easily overcome. To join a raft in a cross current, the newcomer may need to raft on first, then carry an anchor out in the dinghy, rather than the normal order of anchor, then raft.
Multiple anchors are verboten in a swinging raft, so there we like to have the boat with the largest anchor arrive and set anchor first, then other boats tie on. In a stern tie situation, anchors are set from all the heavy boats.
Naturally, there can be no hard rules when you don't control, or even know who is going to arrive next, or at all, so adaptation to the situation is always required.
On an organized vacation, with more boats, we have done circular rafts of as many as 35 boats. There, an organizer was required, as everyone arriving at once would creat total chaos. Once the circle was complete, we had a great venue inside the circled sterns for games, dinghy races, etc.