1 - this is just silly - a vote doesn't get redistributed until a party has lost outright. If there are two parties much bigger than all the others, neither of them will get redistributed, just the small ones will. So as long as you put your preferred of the two big parties first it will make no difference whether you put the other one on at all or miss it out.
If you put a small party first and nothing else, your vote ends up in the bin: you are letting someone else decide. But there is NO WAY expressing a second choice can make your first choice lose.
2 - this is just wrong: it is FPTP where votes get split letting one party win which would lose to either of the others, not AV. In your example you make the same mistake as in 1 - a ballot paper with tory first would only get redistributed if the tories were eliminated so it doesn't matter whether they put UKIP or LD second; they've lost before that gets looked at.
If you had three right-ish candidates in FPTP and one labour candidate, there is a good chance labour could win with 30% of the vote against 20% for each of the three right wing candidates. That would be unfair. While with AV the smallest rightie gets shared out amongst the others and chances are one of the right wing candidates ends up winning.
3 - mainstream parties already try to borrow policies from small parties to get votes - whether green ones or BNP ones. We already have abuse such as Woolas. If we had a more honest / less biased media this would be less of a problem but I don't think we should rule out a better system because of this.
I'm still waiting for an example where 'tactical voting' in the sense of putting parties in a different order from your actual preference will be more likely to get a good result than just putting them in order of preference.
Or for that matter for a realistic example where AV does not give a result that all would agree is fair. And the one where all A voters put B second, B put C, C put A is not realistic - would never happen in real life.