When it comes to arena, it's more about making sure your champs go in the right order rather than having an exact specific number; like you want to put buffs on your nuker *before* they use thier big hit

Having them go as close together as possible makes it less likely the enemy will get a turn inbetween them and interrupt the order.

Speed-tuning is almost exclusively a Clan Boss concept. Don't worry about it much elsewhere. What matters everywhere else is just making sure that your buffers/debuffers go before your nukers.

To your last question, there are only two ways to make your team act before theirs - either have your whole team be faster, which is generally quite difficult to pull off, or have an AoE CC champ that stops their team from acting. The latter is the more usual approach - you use a TM/speed booster, or possibly two, to push your CC champ up, and then have them CC the other team, giving your slower nuker the time to get a turn.

CC being crowd control?  Sorry, learning terminology. 🤣

yep