Quick question. I sided with the dawn guard and at the time wasn't terribly interested in archery; now I am. If I start the Ancient technology quests after completion of the DLC'S main questline, will it re—trigger random vampire attacks on towns? Those things were game breakingly annoying.

I think you should be ok. I never had a problem with random vampire attacks once I had completed the main quest in the Dawnguard DLC.

Ah good, I have done some preliminary testing and it would suggest what you say. I completed some of the quests then fast travelled around different towns, making sure to arrive at night(so as to trigger an attack)and not had one yet.