i've seen a lot of guys come to adult from mainstream. most of what they knew didn't seem to apply here, and most of them admitted that publicly.
take google adwords - there are words adult sites can't use to advertise that mainstream sites can. take the word "girl" - most people i know refer to me as a girl, even though i have a 31 year old son. but i cannot use the word girl on google adwords - even if the ad says "19 year old girls", they say the word girl indicates the models are underaeg. yet any non-adult business can use the word girl.
as far as design, i've seen 5 designers who i actually spoke with and dealt with come into adult from mainstream. they had good portfolios and were even a little cocky about their skills. but did they ever bomb on making their first paysites *LOL*
everyone who's been in adult for a few years isn't a pro - and even if they are, no one knows everything about any subject. during the time that everyone on this board was saying that there was no money in posting galleries at tgps, we were making a living and putting money in the bank posting galleries.
imo no one should ever start taking advice on anything important without going through the posts of the guy/gal giving the advice and getting a real idea of what they know and and what they do.
and that's MY advice ;)