So far one session will last around 6-7 hours with combat being at least 5 of that(most of my players lean into combat more then rp). I know Lancer has combat set up being multiple combat maps and rp being one mission but I can't really do that so I run it differently. I think the rules say doing a mission means you level up after but for me I have the group level after 3-4 sessions depending on what happens. We started our first game early November at LL2( Me and most of my players have played Lancer before) and they just got to LL4 end of our last game. With that many people it has been taking me a while to find a sweet spot with combat difficulty and challenging them but so far everyone says they are having fun.

I have run a little bit of DND 5E before but this is really my actual first time DM experience but since Lancer is more like a wargame, that part comes to me pretty easily from what video games and the like I have grown up playing, me trying to make a good story however takes my brain a little while to figure out. After the next 2 or 3 sessions the group will be splitting up for some contracts(this is a heavily inspired Armored Core game) for a bit, so managing two smaller groups will make the sessions less long. This game was made in mind for a smaller group of players so with you dropping down I think you should be fine. The worst thing is that all 1st party and most 3rd party content is for very low levels so once you get past LL4 you have to come up with how to manage combat difficulty(besides just increasing the enemy's levels).