Ok so here's my tips for smoothly running a pbp I'll probably add more when I think of stuff
-discord is for posting, obviously. Nothing else *just works*
-have separate channels for in character and out character and dice rolls. Have a secret channel for DM stuff, notes to yourself, secret rolls.
-campaignwiki for storing info, character sheets, notes. There's always a chance you can lose stuff on discord and campaignwiki doesn't require a login and you can revert charges if something gets baleeted. Campaignwiki works on a toaster oven and has zero learning curve. Just type and save. Fuck Google drive, editable PDFs and excel all to hell holy shit
-DM should award treasure to specific PCs and update inventory themselves. Most players forget and everyone's gonna have their own way of doing it that'll drive you crazy
-I wouldn't run anything more complicated than swords & wizardry. No BX. The more you have to reference every character sheet before something happens the slower things get. Especially if the players have to reference their own sheets or god forbid each other's.
-have a very simple character sheet template a child could fill out
-simplify inventory. Use slot based, or armor based encumbrance, or just let players carry whatever reasonable amount of gear plus say 2000 coins in weight. Or just do away with encumbrance and adjudicate that shit.
-DM should pick a routine time to do updates and stick to it. A lot of pbp snowball into constant posting, this sucks up an enormous amount of the DMs energy because they always have to 'be on'. I like three to five times a week.
-have a caller. @ them or let them choose what the party does if everybody is dithering/afk
-have players declare routines they do eg when opening doors, checking for traps, and marching formation. Automate everything that happens a lot and have players give you default orders as a fall back like "if we get into a fight I'm gonna move to the back and shoot arrows" or "when we open a room we're gonna let dogs in first"
-don't make players map. Show them the hex crawl, give them a cropped picture of the dungeon room. Sometimes there's one player that really wants to map. It's okay to let them but be ready for them to get bored or go afk for two weeks
-use a kind of zoomed out perspective on Npc interaction. Nothing slows a game down faster than a week long conversation with some obtuse weirdo you dreamed up. If the players are hyperfocusing on something stupid or irrelevant just tell them the thing and move on "the alchemist likes you and will give you the potion for 200gp. Deal or no deal?"
-be obvious about traps, assume PCs are doing the right thing unless they're specifically saying they're not doing that. No pixel bitching.
-do all rolls that could cause harm to a PC in the open, but hide everything else. Don't make the PCs roll for anything other than attacks and saves.
-don't bother with VTTs. Don't make players use software outside what they need to post. It's not going to work for half the people. If you need to do a picture to clarify something either just handwaved it or sketch a pic in ms paint or on printer paper with a sharpie and snap a photo
-offer PCs three or four obvious options, but no more. Theyll get confused and start arguing for days or go silent because everybody's afraid to act, or just pick the first thing the lead player says anyway
-don't pick sides. Talk to the players who don't post often or go silent for long periods. Keep the conversation going. Don't be afraid to boot players who don't post or cause problems. Don't get upset when players don't like the game, don't like how you're doing things, or suddenly quit. Take their feedback with a grain of salt, consider it, and go with your gut.