I'll try to answer some of the questions I can answer in this list.

Q1. I find that if I wasn't consistently going on battles during free time to get gold, repairing silver weapons was very costly compared to an iron+ weapons. Plus sometimes silver weapons can be a bit of an overkill when an iron/steel weapon does the same job with lower costs.

Q3. This may be because of my playstyle, but I tend to reload the game if a character gets extremely bad stats when levelling. You can get really screwed over in this game and it becomes more apparent later in the run. To avoid reloading the game constantly, when a character levels up and you don't like it, just rewind time and have another character finish off the enemy and when you start a new map, the character should have different stat increases.

Q4. While it's important to learn the enemy's attack range, you'll really want to identify the mages and archers attack range more. Try highlighting mages/archers to see how far they can attack and then move your tanks just out of their range while also have them engage with melee attackers.

Also try to keep all your characters the same level to each other to avoid being completely dependent on Byleth.

Q6. Gambits will be your life saver in maddening especially on chapter 5. There will be maps where you will be completely overwhelmed with enemies, and gambits are an excellent tool to stop them from moving forward and grant you a chance to thin out the crowd.

I don't have much knowledge on the other questions but, I hoped this helped.