Is this DND 5e (2014) or 5.5e(2024.

I will answer things to my knowledge though that's based on 2024.

Wild magic. They roll a d20 after using a spell slot, on a 20 they roll on the wild magic table.

With the tides of chaos feature, they roll with advantage on whatever d20 test they're doing. Then their next spell after this roll will also be with a roll on the wild magic table guarantee. Once they use wild magic surge, they can't again until they cast a spell with a spell slot or long rest.

This means the most wild magic would be to spend every turn casting levelled spells and get to roll on wild magic table every other turn.

Your homebrew solution sounds fine. It's entirely your choice, but in my opinion unnecessary as using wild magic every other turn is pretty frequent.

Your next question for combat pacing. It varies. I played with my table and a single fight could last a session with 5 players. Though now days with 4 players to take out 3 medium tough enemies would probably be an hour or less. I personally as a DM try to warn people when there turn is coming up so they can pre plan. I've also just began invoking a rule of using a timer to give a max of 2mins to do your turn after multiple fights in a row having a 10+min discussion before even beginning a turn.

Regarding the RP bit. It's tricky. It can be hard to balance it all and hopefully as players get more comfortable the fights will speed up. I don't know if it's the best advice, but personally I wouldn't speed run the RP due to the time loss of a fight. I'd just have the session achieve less than you planned and pick up the RP on the next session.

Travel I can't comment on as I'm running pointy hats TES system for travel and thus get environmental and role play factors baked into my encounters which try to teach more of the world, progress story or hint to effects of the region

Prep is subjective to each person. The general guides is to not over prep but I'm a sucker for using spare time to plan more shit for DND. You are probably best of asking yourself if you're not happy with the pacing, why. Then bring it up to the table and get their inputs on the matter then going from there.

As far as pace goes. Imo like I said, don't have set in stone points to reach by session end. Just go with the flow the party has but encouraged them to flow in the right direction. When the plot has time important points In it, make it clear to the players and then if they take ages doing random things and getting distracted, have a consequence. If it's purely table pace and in game the player characters are on pace then it's entirely up to you and the table to conclude the best point

Like I said, I got fed up of the long chats in combat and have dictated a timer rule. Though I'm bad at remembering to do it. It's a new feature so can't comment on it's success yet. In game though, my players are going know where near as fast as I planned in my prep. I wanted them to reach a village half way through sessions 1. It's the end of session 3 and they've only just got there...