Funny, the numerical ordering of you questions.
1. I have heard a tiny fraction of what's out there (I've heard lots and lots, but it's still a tiny fraction), but I do like Ascend speakers at the price point (not pretty though), and as for used, I'd consider PSB Images if the used pricing is good right now on the previous gen. They don't quite image as well as Ascend bookshelves, I think, subjectively, and are maybe not quite as clear on the top end, but they can pack a punch for what they are. (They're not big ugly commercial speakers, and they're not designed on an unlimited budget.)
3. I would definitely forget dipoles in your situation. Now if they happen to be available in the lineup you choose, incidentally, and you REALLY want them, you can save towards them. But know that dipoles are best used in rather particular setups (start googling and searching around if you want to know more). I would prefer (just as much out of necessity) bipoles to dipoles for surrounds, and currently use bipoles, and even with that said, I think either* are overrated for surround use- I guess I don't much stock into "surround design". (You can find some that are switchable between both modes.) It REALLY is about the front three speakers, both in choice, and in placement. The steering of audio within the front three, the dialogue, the impact, etc. My opinion only, of course. But finally I get to the most salient point I wanted to make: dipoles or bipoles for that matter just simply will eat up too much budget; they have double the woofers and tweeters, and that obviously comes at a price. Now, if your budget had an extra zero next to it, sure, go for it! Or not even that much, but I think it's just too tough right now to think about.
2. It depends. You could for the meanwhile measure your db levels obtained/desired at your LP, measure the distance from ears to speakers, and a bit less importantly, the dimensions of the room. Then someone may have an opinion on the need for external amp with a specific candidate for speaker in mind.