I can't answer as a good player only as a noob, who had similar questions just a month or so ago. This is all "advice", so its not scientific, just what I've come across.
1. To me, take as much time as you need to assess the board. I suppose at some point, the delay is intrusive, but its probably much further than your gut is telling you to "get going". Take a few minutes at least, tell the opponent this is what you are doing if you must. DON'T let people pressure you too much, I get this a lot on iso and the more pressure I feel, the worse I play. Don't fall for it. Don't be obtrusive with your delay, but taking a few minutes is understandable, just let your opponent know this is what you are doing.
As an aside, discuss moves with players. You'll find most opponents don't give a rat and will largely ignore you. (ASIDE: A lot of players on iso want lots of games fast, in particular there are some low-rated players who play really well, but also really fast. My theory is these are advanced players, who have created a new account to get their rating up, with a nice clean record along the way). The players who DO stop and discuss though are INVALUABLE. You won't find those players though, without at least trying to discuss a move or two.
Also discuss the games here from time to time, especially if you thought you played a good strategy and lost, but are unsure why. Use CouncilRoom to post the results of the game and then ask how and why the game went the way it did. You'll learn a lot.
2. I can't answer for high-rated players, but I can guess. I THINK the rating system can really punish your ratings if you lose to a low-rated player, and certainly playing with an unregistered player, isn't the kind of thing a high-rated player is looking for. But I can't really answer, I get CRUSHED regularly by players just in their low 20's. CRUSHED. So, my perspective isn't only noobish, its also from someone who really can't play very well at all.
3. Solitaire is useful, others here taught me to test strategies out to 4 or 5 provinces, seeing how many turns it takes, then attempting to beat that with the same board. However, solitaire is also misleading. Part of the reason I went on a massive losing streak lately, is because of solitaire with Hinterlands. It isn't the best way to learn new cards, because it's not really battle-tested. You never have an opponent trying to stop you, or competing for cards, so it can produce skewed results. Use solitaire to assess a board and get a general sense of what works, but remember your opponent has a HUGE impact on how the results eventually wind up. The times I played solitaire most, were ironically the time I started to get smashed in the ratings, dropping from 18-13, where previously I was climbing steadily. Solitaire IS useful, but I was taking the results to heart, rather than just actually playing real people and learning the right way.
4. I can't answer this last one, except that the creator of CouncilRoom stated that one way to help him is to spot bugs and report them to him. The other is to petition the new pay-Dominion site that is coming, to release logs similar to the ones that isotropic posts. So in other words, a little pressure from the fans, can help, when the time comes.
My isotropic name is ChaosRed, if you want to run a few games (practice or real) let me know. I look for people willing to discuss the game, as much as play it. I am not very good at Dominion, so I compensate by accenting the meta-game more, making it a more social thing. The real players on this forum are way out of my league.
And good luck out there!