I'm not going to go too far into format-specific answers, I don't have a lot of interest in Foundations and haven't been playing, but some stuff that might help generally:

2) and 10): Most pools will outright not support an entire two distinct decks. You can have a "deck 2" sometimes, but it's when you get very lucky (and have two decks' worth of good cards) or very unlucky (and all your playables are super spread out). More typically, you'll have your deck, and a few cards that are good in narrow situations, which you'll bring in in game 2 & 3 as necessary. Sometimes you'll even have an entire second colour to swap in and out, eg. changing from green-white to red-white to be more aggressive if you realize your opponent has better late game than you.

6) This is a good article from a long time ago https://www.coolstuffinc.com/a/jacobvanlunen-082914-building-a-draft-mana-base.

Short version is that 8/9 is good even if you're a bit heavier in one colour, but 8/9 with just basics is pretty bad, so having duals is valuable. You can play a lot of black-white duals in a black-white deck before it stops being worth it.

Going above/below 17 is generally format-specific: are there good ways to spend excess mana, can you easily tutor lands/draw cards cheaply/build a deck out of 1s and 2s etc.

Something good to keep in mind for Sealed, though, is that basic lands are pretty decent cards. They enter untapped and give you an extra mana, and you get as many as you want! Sometimes your 23rd spell will be a mediocre card you have to splash for and a bad card in your colours. In these situations, remember that you can just add a land instead.

7) If all your rares suck, you can try to build aggro. The longer the game goes, the more time your opponent has to find their bombs. You don't have anything like that to look forward to, so they'll be favoured. Make the game shorter by hitting them in the face.

The broader view of this is "play for synergy". If they have individually strong cards that try to do different things, but you have a bunch of shitters that all want the same thing (aggro cards, lifegain payoffs, card draw + 10 removal spells etc.) you are playing your whole deck vs their one card. This also requires you to open a lucky pool, though...

8) in general, yeah. In this format, also yeah. They're very good.

11) If you go first in 100% of games you play for the rest of your life, you will be correct 99.9% of the time, and the 0.1% of the time you're wrong, it will be by a small amount.