sweet lamb is open, but you cant get close to the action,
the best stages are the ones up in the mountains/forests (they are not to dark at all, the roads are fairly open and give plenty of light enough to take pictures anyway), go to the spectator spots and just have a walk around, its amazing how close you can get, you should to get there really early, take a flask, and wear thermals, and a packed lunch waterprrof trouser and hiking boots,
tickets are bought from the wales rally gb website, and imo are reasonably priced for top flight motorsport, depending on tickets parking should be included, effectively they just park you up on the side of the road, you need a good map reader to get to the locations.
as for equipment, you will want a zoom lens, spare batteries, and if you go to the service areas a general purpose lens like a 24-70 or something.
I been a few times, kinda what got me into photography, been meaning to go back for the past 2 years but life commitments keep stopping me, one day i'll get back.