I'm going to respectfully disagree with a lot of this (swanning_it's post below). I've been twice in the last 3 years, 5 nights and 8 nights. I agree that it's an amazing and relaxing place, and an excellent place to holiday. But:
1. Agree. Upgrades are rare but improving for diamonds. Used to be no reports and now there is the occasional report.
2. April May are low/lower seasons and you probably won't need to book much in advance. Both my stays were in high season in December and nothing was booked out. Don't over think/plan it unless you have somewhere you really want to go on a specific night/event.
3. Fully agree. Including your flights (basically compulsory 500ish USD) you'll probably spend 1000-2000, if not more, per 5 nights per head.
4. Agree, upgrades are possible to buy, I like the over water for the experience but it definitely has downsides to the beach villas.
5. I've been to Ithaa twice, one lunch then a dinner. I really enjoyed it and the food is decent. Horses for courses- I'm happy to pay for good food in a location like this, but I'd never buy a $50 wine...
6. Do you mean the coughtail hour in lieu of an exec lounge? If so, I agree. Free drinks, though I think I only went twice.
7. No idea
My room pref is for anything that tickles your fancy. Ever been in an OWB? If not then get one. If you have, the base beach villas are decent. I haven't been in an upgraded base villa, nor in the deluxe ones.
Full breakfast is available on either island. It's full buffet on the main island and Al a carte buffet on the other.
Snorkelling is the main free activity, they give out the gear free at the shop and you return it at the end of your stay.
I generally swam from one island to another but you can walk across on the bridge (500m) or take the free dhoni, which is a fun little novelty the first time.
Conrad Maldives was possibly our most relaxed, yet invigorating holiday yet. We spent 6 nights (from memory) and loved it.
I can't comment on your time frame (we went in January), but to be updated on the realities, I offer this precise,
1. Room booked will likely be the room you get. Having said this, the base beach villa is superb by any standard.
2. Tours/restaurant bookings need to be done early. If you leave it to see how you feel on the day, the chances are you'll miss out ... especially for Ithaa undersea restaurant.
3. Tours/meals/drinks are expensive. Be prepared to spend money if you want the full Conrad experience. (our spend for 3 pax. was approx. AU$15000 over the accommodation redemption, but this did include multi upgrades (2 nites over water premier villa + 2 nites beach deluxe + 3 nites beach villa) and various water activities included jet skiing, island hopping, whale sharks (yes, including swimming with 2 whale sharks) etc...
4. Upgrades can be negotiated over and above the base rate. I'm only going from memory, but an AU$2400/night room cost us an extra AU$600 a night over the base redemption. Yes, expensive, but no where near the full rate and well worth the experience. My personal preference is a beach deluxe. Very nice, but still a reasonable rate.
5. Ittha is OK, but not worth the money. It'd be nice to eat in the fishpond, but a morning tea is possibly the best value.
6. Happy hour over on the "little island" is good value.
7. Don't let a 14YO have "mocktails" as they're just as likely to be "coughtails" and you'll have a staggering, blithering idiot as a child for as long as it takes her to pass out!