kudos for having courage / determination enuff to invest time, effort and dollar into starting this little pass time of our's!
i never got a lesson and i never rented, having also pig headedly dived in, just to keep up with the skiing in laws one xmas! i have been addicted ever since and even got qualified as an instructor and so someone as well versed in balance sports
as yourself should have no probs!
however, having an expectation based on other, similar experience / skills can be a double edged sword. there is an element of familiarity, but there is also a real risk of over confidence. having said that tho, approach it with modest expectations (ie walk before run) and you'll be carving black runs within a week or two!
with this in mind.... there is no harm starting out on a beginner / intermediate board; ie a soft free rider. IMO. i haven't ridden a shedload of boards, certainly not ones appearing in the stores now or soon, but i am sure you can get a good idea of what's what. TIP - stiff boards ain't for you. not this year.
as far as the nitty gritty of teaching your self; simply do the following - (very basic lesson plan here for which i will get strung up):
suss side slipping
swinging your shoulders to initate turns
.. i reckon the rest will be for you to sink or swim!