TTing backwards or forwards should not change your friendship level with villagers. It just gives you the "haven't seen you in a while" dialogue and obviously you lose the opportunity to increase the daily friendship points you get from talking to them or gifting them. But TTing in and of itself doesn't affect friendship levels.
I TT'd quite heavily for a bit while cycling out villagers and I still managed to get four photos during that period. In fact, it gives you the opportunity to give them more gifts than once a day, as even going back one day and back to the present will reset the gift-giving option.
Nope. Even if you don't talk to them for a while, it doesn't affect friendship. It's thought that maybe talking to them many days in a row is supposed to (based on the code), but it actually doesn't (maybe because it's glitched, who knows).
