Yep, the 10 in 4.5.0-10U specifies that you have a browser which is currently on v10. You can start from this section (Part 2), and work your way onwards.
.... Eh? I can't provide proof, but what I said can suffice as proof until someone who actually knows something about 3ds hardware can come along and disprove it. :P Very unlikely, I know.
If one of the SD slot pins fail (as OP is using a CIA) it could crash upon trying to load certain level aspects. This is highly unlikely, I will admit :3
Things like the game card slot can fail and the 3ds can still boot up. Screen ribbon cables can become damaged and the system can still boot up. There are many things that can happen hardware-wise, and the 3ds can still boot.
This. Most of the available "dev" apps we have where either leaked or dumped off of a 1.0.0 NAND. Try to dump your NAND, you never know what Nintendont might have left behind.
According to the sites you linked, yeah. I would go the silver, as you can always get a9lh and update to 11.0 while still being able to use your flashcard.