i can only go by what i have done when i have been to ibiza, i tend to try and visit all the best nights/days that are going on when im there for a week or two, i tend to go to pacha quite alot and if you staying in san antonio then i would recommend getting your pacha tickets from cafe mambo as all the pre-parties for the pacha nights are at mambo and with every ticket bought they offer you a free coach to pacha that leaves around 1.30am just at the top of the road from mambo. you have to fing your own way back though, there are plenty of taxies outside most clubs. and buses. mambo's ticket prices are always pretty reasonable and you also get one free drink in pacha with mambo's tickets. but for all the other clubs, no matter where you are staying on the island near enough everywhere sells club tickets for every club, even at the hotel reception, or the local shop. so they are so easy to come by. every bar sells them, and wherever you buy them you wont make any substantial savings as some sell them for just a few euros cheaper or dearer so you wont be too out of pocket.
i have never bought my tickets online before i have gone, but thats just me, im sure you would be fine getting them online. but i have been to ibiza 8 times in 9 years and i have never had any problems coming by tickets on the island, so dont worry too much mate. you'll get your tickets easy in ibiza.
as for vegie food, i aint got a clue, ibiza has some fabulous restaurants that cater for all tastes so ul be fine.
just enjoy your time there, im sure u will end up going back, as i have done. i was 17 when i first went to ibiza and it opened up my eyes so much, im 25 now and i just love ibiza as it has so much to offer everyone at whatever age you are. ibiza is like no other place youl ever visit.
