I started a game where the players were 5 thiefs and an assassin, so it seemed like a good idea to set up a Thieves guild game where they were all from the same guild but it folded pretty fast despite the characters picked it was perhaps not what they were looking for.
The start of out of the abyss is actually ok to pick up and run. Just read the first place the group are in carefully and you are ready for several sessions. After that you would need to ask the group where they intended to go and then you can plan the next things. If you level the group in...
The whole drow tracking the party across the entire underdark thing is a bit weird anyway. I mean why would they bother. I'm not sure it adds a great deal either.
I agree the 4e Christmas tree of magic items was silly. I tended to just play in a low magic item setting and use the natural bonuses. This way if they ever found a magic item I could make it something reasonably special and unique and not just +2 to hit gives you +1 damage if you happen to be...
You might possibly want to play Gloomhaven.
In this not really much of a roleplaying game game you can swap the characters out depending on who turns up. Each player just needs one character. Bonus you get to play and not DM. This may not be what you want at all if you in fact want a...
Oh and somewhere you mentioned the software was slow. That is the problem of moving big files around on the internet. If the software is not connected to the internet it is inherently much faster.
You can make your own maps in maptool or drag and drop maps you already have. I am completely hopeless at art type things and I was able to make a passable house with a removable roof.