I use Roll20 for an in-person campaign at my place. If you can swing it, I think you'll want to try to get everyone on their own device. I have three players on laptops and two on tablets, all sitting around my place. If you're already going to be on R20, there's some significant advantages to everyone having their own screen - which is, of course, how R20 was designed to be used. Line-of-Sight is the probably the biggest factor; it's one of R20's best features & that's going to be completely nullified by using one computer for all players. Having customized macros for each PC is nice, too - you could have that using just one device, but the trouble is 3-8 players crunched around one computer keyboard+mouse. I think each player's ability to use the R20 functionality is going to be pretty limited with the bodies/keyboard-mouse ratio. You're not really going to be able to use PC character sheets on R20, again because one player can't check his sheet on the screen if 2-7 other players are sharing that screen. Using R20 character sheets is nice because that's where the macros pull information from. I can understand being hesitant to tell your players, "Bring a laptop or tablet that'll run Chrome, Firefox or Safari"...but I would suggest that's what you're going to want to do or at least work towards...and, of course, you can help try to borrow one or something for the session. I borrow one laptop for one player to use that doesn't have anything to bring. My two cents