Typing on phone. Please excuse any unintended terseness. 😁
1) You can do quite a bit with the standard patriot. If I could only have 1 brush, it would be that one. If you think that you will be doing more details, then yes I would probably try to get the Sotar too. For example, I prime, basecoat, and zenithal highlight (a 3 color stack) with the 105. For weathering (inks and washes), touching up shadows, adding glow effects or fixing highlights, I reach for the sotar. All if these things can be done with a hand brush if you're determined to learn the techniques (I'm not, haha).
2. No extra needles. I run our patriot box stock. I have other needles for the sotar and have never used them. On a few occasions, I've used both brushes in the same session, i.e. popped the patriot off the air line, slapped some ink in the sotar, and then proceeded to fix the huge mistake I just made, hah. Then took off with the patriot again. This would be moderately less convenient with swapping needles. But again, think about your anticipated usage scenarios.
3. I haven't had trouble priming (clogging) with the std needle, but I clear my brush with full on blasts to a paper towel every few minutes. This blows all the crud out (paint boogers 😉). I shoot a lot of black, and yes they do shoot easier than white primer, but after some experience it all works. I have had trouble with some bright silver metallics flowing well, but never enough to thwart what I was trying to do. The metallics just "feel" different, and require some patience and a little heavier trigger. (I shoot silvers out if the sotar too). Side note.. clogs sounded really scary when i started. They are truly not a big deal.
4. No experience with the patriot extreme. I've got limited time on the Krome, which is very similar to the sotar, but from memory a little heavier.