@Arkandel
For me, a D&D Mush can be played two ways. it can be played as a standard D&D experience, you get a few friends, collect on a day of the week and run an adventure that is set within the continuous world provided by the MUSH setting.
For the second part, it allows you to do more lone-wolf stuff, or be a sword for hire, or perhaps just be a noble that might on occasion hire some adventurers to go see the world or look at a piece of property you might be buying to make sure there's no goblins or ghosts around the area. You can do a bit more political if you want.
The main thing with a D&D MUSH is that you're going to need pretty constant GM oversight, with a small game you have a dedicated team that can work in shifts of 2-3 people at the busy times and try and have at least 1 on during even the off hours. As the game grows you can slowly bring in player ST/GMs that can run events for players and forward information.
One of the biggest drawbacks to GM'ing such a large game in a continuous world is data, it is really hard to keep everything straight. This can cause setbacks or retcons all of which suck but come with MUSH'ing in general.
As for houserules, I don't think a whole lot needs to be made right off the bat, but should be looked at as the game is played. You could maybe mitigate somethings or just remove certain aspects/spells that might muck up what you're going for. Generally the biggest houserules that end up happening in a tabletop>MUSH is in regards to PVP. Thankfully D&D pvp is pretty straightforward and less convoluted than other tabletop systems since playercharacters are for the most part treated just like any other creature/character when it comes to spells/abilities/etc.
The biggest struggle I think for DND 5E going into MUSH is that of the players themselves. You have to go into it knowing it's not quite going to be like playing it at home or on website like Roll20. One of the biggest drawbacks is how the D20 systems are so spatially oriented (exact distances and LOS and stuff like that), that is hard to bring into a MUSH. Some MUSHes that run D20 systems have built mapsystems into their game so a GM can whip up a map and try and keep everything in place but they are not always pretty. A lot of it comes down to just being clear and concise as the GM when speaking about distances and positioning, taking note and making sure to keep track of any battlefield changes, and for everyone involved to be patient when it comes to people asking questions.
That said, when it comes to social/political stuff, D&D is actually really simple which is both bad and good, it pretty much boils down to a couple contested rolls and good/bad RP, which is OK when it comes to NPC>PC stuff, but PC>PC arguments are never easy to settle in D&D mechanics, it can really make people feel cheated in a way if they get a few bad dice rolls and think their character has to agree with what is being said. One of the best ways to combat that however, is to have a realization that just because you lose the dice roll, does not mean your character is forced to believe or agree with the winner, but it does mean that for all intents and purposes, the winner of the dice roll has won the argument. The character that loses does not have to agree, but the end of the rolls signals and end in the discussion, so it becomes time to agree to disagree or just to walk away.
This got a bit longer than I intended but there are some of my ideas and thoughts on what you proposed.