1. As in modern and SF games more generally, you might find a strong melee attacker causes a surprising degree of problems - targeting a resistance that isn't favoured by most PCs and doing big damage that starts knocking people down. I've seen Alternity PCs mow through multiple light to moderately tough enemies, which is not necessarily a bad thing, if the GM has plenty more.
2-3. I ran a couple (edit: now I think about it, three) in-person sessions with prepared adventures for three or four players, and a longer-running Dark.Matter Play by e-Mail that ramped up to three groups dealing with loosely related storylines. Online play saw a lot of people leaving or wanting to start in comparison to the pace of play, which still seems to be the case now in different systems and media.
4. A large party will have an easier time, particularly when they all act in coordination. I haven't run a game myself with more than one character in the same party, but I see interesting possibilities in a player having more than one character with different roles
5. My Dark.Matter game involved chasing trails of clues to past events with periodic encounters, eventually running into creatures. Players brought about several events, from my perspective, mostly by their own choices - which also seems to be a common experience of other GMs, as others may remember from the Quickie Mart Massacre story.
6. I found handling of Achievement Points was pretty important - what you choose to reward and how steadily you want players to see advancement and new options. This post has been edited by uncle_jimbo on Feb 23 2018, 00:59