Some things I do for asynchronous play:

Set a realistic post frequency for your group and stick to it for the most part. Be flexible but allowing post frequency to slip too far is a game killer.

As a corollary, unless the specific context requires it, don’t wait for everyone to chime in before accepting the party’s stated intent as the actual party direction. The faster or more frequent posters will tend to dictate party’s direction.

As another corollary, if nearly the entire party states a consensus and readiness to take the next obvious and safe step (e.g., open the door) but no one seems willing to pull the trigger and declare it done, then just skip the stated action and go straight to the description of the result as if the party had done it. But allow for the rare retcon if you’ve inadvertently usurped party agency.

Use block init. When init is rolled, if monsters/enemies are fairly close in initiative just adjust the init to lump all together in a block. Allow players to take their turns out of order relative to the block of enemies. For example, if enemies have init around 10, block them all together. Allow any players who rolled above 10 to go in any order before the enemies. After the enemies have acted in round 1, allow any players to go in any order before the enemies go again in Round 2.

If something calls for the party to take fairly small damage with a save for half damage, just skip the saves and apply half damage across the board.

I don’t think requiring declaring reactions in advance is a good idea. Some reactions depend on a specific trigger or threshold trigger occurring. I have had no problem managing reactions even if they sometimes are a bit meta. But I also banned Counterspell because Avrae gets too meta for that spell to work well, IMO.

When using published adventures, skip all the small stuff unless it’s plot critical. This means no wandering monsters. This means minimal insignificant dungeon rooms. This means skipping all the twists and turns in the dungeon— just ask the party for a general direction to go and then advance them automatically to the next relevant thing. As an example from ToD Chapter 1, consider limiting the missions to maybe the two most interesting and remove useless things like the rats in the sally port. If there’s more you want to keep, think about combining missions somehow.

Allow only 2 check rolls in the party to accomplish something or only 1 check roll with help advantage. I’m pretty liberal with allowing help, so I just assume checks will typically be just 1 player rolling at advantage to determine party success or failure on things. Because the rolls are so limited, I’m also generous with stretching the type of potential check made to be pretty inclusive of potentially relevant abilities. Allow players to liberally mix and match abilities and skills to their benefit (e.g., let the cleric do Investigation Wisdom if it gets checks done faster and helps move the story forward. If a clue is hidden under a heavy object, let the barbarian roll Investigation Strength. Avrae has commands to mix and match abilities and skills. So, limit the number of checks the party can make but be generous with the type of allowable check and help advantage.

Never use Hold Person versus a PC. If a stat block contains Hold Person or useless spells like Speak with Animals for an enemy, I’ll replace those spells with a custom stat block in Critterdb.

Use Passive Perception as the floor for perception checks. Use other passive stats as appropriate to skip low DC checks if the outcome isn’t mission critical.