I can give you some answers;

1) Depending on where and what you eat you can expect to find some items on the various menus in the price ranges you mentioned, although your lunch prices are a little low - realistically you'll probably spend more like $10 to $15 PP at lunch. $5 is only going to you something "very light" or "very simple". Dinners can be done in the $20 to $25 PP range. You will have to steer clear of the more upscale restaurants which will run you double the prices you mentioned.

2) Groceries will run about 25% to 30% more than you probably pay in the Toronto Area.

3) There's no "town" in Frigate Bay - it's mainly just resorts, plus a convenience store, a couple of souvenir shops, a wine store and a couple of restaurants and a few beach bars. Most of the beach bars and restaurants will be open Christmas Eve some may or may not be open on Christmas Day. Don't count on the shops to be open on Christmas. FYI - The main "town" on St. Kitts is Basseterre - a 10 to 12 minute drive from Frigate Bay. most of the stores and shops in Basseterre will be open Christmas Eve (some may close early) and almost all will be closed on Christmas.

4) Rental cars are usually available on the island but Christmas week is a very busy time on the island for tourism so rental car COULD be scares. It's best if you reserve one in advance. you can find a list of car rental companies with contact info here: www.stkittstourism.kn/explore-st-kitts-getting-around-car-rental.php

5) Yes, daytime temps should be in the low to mid-80's F. Mosquitoes are not usually a major problem on the island, especially in December when there are nice breezes which help keep these pests at a minimum. You are dealing with Mother Nature so there are no guarantees.

We have a timeshare at the Marriott (10-15 minute walk from Timothy Beach Resort) and have been going to St. Kitts for 10-12 days the past 5 years every January. The weather has always be great, temps in the mid-80s (one day of rain in 5 years). We've never had a mosquito issue. Timothy Beach is right on the Caribbean and so are several beach bar/restaurants for lunch and/or dinner. They can be fun and inexpensive. There are fabulous restaurants as well on the island at US$50+ per person. The Marriott has a casino, several restaurants and music in the evenings. I agree with the first reply as to prices.

I would urge you NOT to rent a car. Driving is on the left, roads are narrow and not well lit at night. There are many taxis around the Frigate Bay area all day and night. Rates are set by the government and are based on zones, not metered. Fares are very reasonable and the drivers also make wonderful guides. I can suggest two drivers: Sackville Grey, sackvilg@hotmail.com and Debbie Carty, debbie-99carty@hotmail.com. Both are extremely knowledgeable of the island and very dependable (they'll give you their cell numbers so you can call anytime).

Check the websites below for more info.
http://welcometostkitts.com/general.php
http://www.discover-stkitts-nevis-beaches.com/caribbean-beaches-in-st-kitts-nevis.html

Have a great time!