I did not read every page in this giant thread, but I'm going to give my opinion on party size.
Ok, I'm fine with 4 in the main party, but I really enjoyed the extra followers, like Sazza and Glut. From what I've read on other threads, they're talking about later having mercenaries in the game. I'm not sure if this is just to give the player the option to have a fully customized party in single player, or to replace fully dead companions or ones who get mad and leave (or leave for any other reason).
I think that a customizable "throw-away" follower or multiples of them would be awesome. Ones that actually stuck around. Maybe even ones I could train. Say I had to take a group of recruits later on and train them with my party who later help in large battles, I don't know. There's a lot of options here. They're not infected and might not even have a major role in the storyline.
I'd also like to see multiple long-term summons like familiars and ranger pets. Having them customizable would be cool, too. Say we got to name them and possibly give them equipment, even if it were limited like a necklace and a ring or something. I should be able to summon both a familiar and my animal companion as a ranger, and everyone in the group should be able to summon at the same time.
So in total, it'd be 4 companions, 3 mercenaries, and up to 4 familiars and 4 animal companions (if they were all rangers). I know that's a lot, but the game is already starting off with very large fights and I'm expecting even bigger ones later. Imagine fighting a gargantuan monster or even several huge ones like a fire giant camp without having a ton of bodies to throw at it.