As a Brit, but neither a specialist in the medical area nor a teacher, I can only try to assist on the 1st two:
1. I would always say "roast chicken", but there is a similar expression "broasted chicken", which, I believe, is boiled first.
2. The way I would differentiate between a "medical assistant" and a "nurse" is that I would expect the nurse to be highly trained/experienced/qualified in their chosen speciality, and capable of assuming responsibilty for their actions. A medical assistant, I would regard as being an unqualified "helper", who handles simple routine jobs, that don't need specialised training, under the direction of the qualified hospital staff. The assistant enables the qualified staff to concentrate on the matters that require their specialist knowledge/experience.
In AmE, "dating" sounds more like "day-ding" than "day-ting," although it's a very subtle difference. Pronouncing it with a hard T sound (day-ting) won't immediately brand you as a non-native speaker as would, say, pronouncing a hard T in "butter" (in AmE it's definitely pronounced "budder." )