I got married abroad and we just let people do whatever they wanted and come to our Wedding on the day. Will everyone be travelling with you or will they be travelling on different days? We had people arriving on different days, so we tried to meet them when they arrived and made sure we spent some time with each of them before the day itself, even just meeting up on the beach for a couple of hours or going for a couple of drinks one evening.
I wouldn't necessarily plan a 3 day itinerary as people like to do different things whilst they're on holiday, but you could maybe arrange a pre-wedding meeting so that everyone can meet each other before the day. This could be a day trip - a trip to a vinyard or a boat trip maybe? (if it's outdoors, make sure it's a couple of days before in case anyone gets sunburnt) - or you could arrange a nice meal in a local restaurant one evening where they have some organised entertainment for your guests to enjoy? The reason we didn't do something like this was down to cost - I'd feel cheeky inviting people to do something and expecting them to pay, but most people had met before the day and it really helped as we only had 24 guests so the atmosphere would have been lacking somewhat if everyone wasn't mixing together.
You could also make up little information packs for your guests of various things to do and places to go, and just put a little covering note welcoming them and saying "We're doing this on this day, that on that day and such and such on the other day - feel free to join us if you wish". That way people know what you're doing and can pick and choose what they want to do. People won't feel obliged to do what you're doing if they don't want to, but they also won't feel left out as you've given them the choice. I'd also include some useful information like the nearest shop, pharmacy, cash point, car hire place etc. This information can sometimes be a bit hit and miss from holiday reps (if you're booking package holidays at all) and your guests will appreciate the extra effort you've made to make their holiday more comfortable and enjoyable
I hope this helps a bit
getting married abroad was the best decision we ever made as the big family holiday and big party when we got home made the whole time surrounding the wedding day much more special, it didn't feel like a big build up to just one day which was over too quickly. Our guests loved it too, we recieved thank you cards from THEM when we got home!!!