"1) lets say I find a field of research that interests me at the undergraduate university, and I gather a lot of experience in that field. Is it true that after im done with undegrad, I could relatively more easily get into the PH.d, program under that professor?"
Depends on the admissions committee. Some people think this leads to intellectual incest and actively discourage undergrads from the same school from joining their grad program. Others may later view it as a lack of ambition on your part. Also, if you start as an undergrad, depending on how long your grad career runs for, you may be working with this guy for eight to ten years. Chances are, you will get really fed up and bored with your work by then.
The best way to get into grad school is to demonstrate that you are interesting, intelligent, can work your ass off, and (maybe the most important) can bring in money. Start doing outreach work, find someone who will let you at a bench, make posters and bring them to conferences, apply for fellowships. This stuff will go further than even the best admissions essay.