Well, the cottages in the Salty Springs lot are not needed to run the resort - Sims are using them, sure, but only the resort tower is actually needed.
I want to point out that a lot of Sims 3 gameplay and features are bugged and sometimes heavily. There is no reason why this shouldn't be true about Island Paradise as well. The world itself runs extremely poorly and becomes unplayable after a while - even with the route fix mod and whatnot. And also, when all packs are enabled, there is a much greater likelihood of getting script errors, and the game just getting things messed up.
The only other pack I have played with in this resort project is Pets in one save - restricted to a few pets in my played household only. This is intentional, because I want to know exactly what features the pack in question has. If I played with everything enabled, there is a risk I would get confused and be unsure of what came from what pack.
I believe it is important also to note that no packs are depending on any others to function. All packs are purely optional and only require base game be fully experienced.