I'm only level 14 currently but here is my take on the difficulty and such.
2boxing is great (even without MQ) because it allows you to essentially have more power per person. I have had no difficulty leveling so far and don't really see any problems moving forward in regards to grinding xp. With that being said, I really wish the box limit was increased to 3. I know it isn't super popular but I play my own unique way/times/have my own goals and tasks. I can't be relied on and cannot rely on grouping just yet. Having another character would give me a little more power and diversity within the group. Not having a "tank" will inevitably suck as I get higher up (just like in every game). Again, my problem to deal with.
The raid size of 18-24 (can't remember the exact number currently) is a little concerning due to how the population of newer servers is. I could understand 12 as average and 18 as max but I'm hopeful that this will all work out.
You bring up not needing to sit for 4 hours straight per session. I have had 0 issues walking away for hours at a time. My girlfriend/dogs are constantly pulling me away so camping or AFK'ing isn't really slowing me down. Don't rush the journey. Take your time. So far the only "time sink" has been my Gnome Cleric's newbie weapon quest. Even then, I kill a few things and come back to the pc like 10-15 minutes later.
The server seems to be fairly solid overall from what I've experienced/seen on stream.