1/ I get your reasoning, but I don't think it's a good idea. There will be cases when the driver market doesn't offer that many options. If you want a particular driver (be it your favourite one, rank, age, etc.), you might not be able to get him simply because of his nationality. It isn't exactly realistic either. While I do agree that it doesn't happen that often, it's not like it never happens. Tyrrell used to have 2 French drivers, Ferrari as well for 1 season, Sauber and Jordan had 2 Germans, Brabham, Arrows and Toleman had 2 Italians etc. (A bit in that regard, the last Italian to drive a full season for Ferrari was Alboreto in 1988)
2/ ytho? Not like this doesn't happen irl. Plus I think your concept has way too many flaws. You don't consider at all that drivers aren't locked in their ranks. Take my lineup right now. I signed both Andretti and Peterson as B drivers. Peterson is already A, while Andretti probably soon will be. Now assume I signed Peterson as 2nd driver, Andretti as 1st. Andretti's contract runs out first, so I have an A driver as 2nd. Allows me to get another A driver as 1st, or a B (soon to be A).
Or the other way round, I have an A driver as 1st and B/C as 2nd. The A drops to B, the contract of the 2nd runs out. How to get a good driver now? I'd have to pay PP to drop 1st to 2nd, which probably screws me just as much as signing a mediocre 2nd driver.
And it's not only because of T1 teams that mid teams struggle to get top drivers. T4 have priority for rookie signings, quite often locking some of the (soon to be) top drivers for 4 years without making any progress themselves.
3/ Right now, from Tier 1 perspective, there's simply no point taking the win sponsor imo. At best, you'll win all races of 1 track style (which is incredibly unlikely to happen), so 14-18 PP (depending on the amount of tracks with the respective style). Taking the top 5 sponsor, you'll very likely end up with at least the same amount of PP, probably even more.
For tier 2, imo, the win sponsor is out of question. 2-3 are the maximum you might get. Top 5 is an option if you have a decent lineup and plenty of PP. But even then, you'll probably only get the required results on 1 track style. So you might as well go with Top 10, and bag in the income on almost every track, giving you about the same in total earnings in the end.
Can't say much about Tier 3, haven't been there yet.
As for Tier 4, I guess the general stance is that since you can't drop any further, you might as well risk top 10. Take into account the high dnf numbers, plus the T4 rookie bonus, it isn't even that risky picking it.
4/ Since everyone can only rate your post once, you shouldn't count the ratings, rather have people reply.