We have been on the Royal Clipper several times in the Caribbean - including the Grenadines. (1) Yes - you can explore independently. (2) Yes (3) On all (or all but one) of our trips we have been in Cat. 2 - at our own request (ask for one amidships). Cabins are well fitted out with good quality fittings.
Apart from sleeping etc. you are unlikely to spend much time in your cabin. Instead - on deck watching the action, the tropical bar (the main "social" area), on the open part of the bridge and adjacent thereto, maybe once in the net under the bowsprit, maybe once climbing the mast to the crows nest (with safety equipment).
A couple of suggestions:-
1. On the day of embarkation, boarding usually commences at 4.00 p.m. Dinner usually starts at 7.30 - suggest you go in then (the Maitre D will help you to a suitable table) and be out by about 9.45. Make your way up to the area by the open part of the bridge ready for sailaway at 10.00. The sails are being raised as the ship leaves the port and then you will have the Trade Winds coming from astern of the ship - yes, real sailing. Listen as well as watch - can be emotional !!!
2. In St Lucia (time permitting) definitely go ashore at Marigot Bay and walk around there and, maybe, have a snack / lunch in one of the cafes. Marigot Bay is a very historic bay for sailing ships to shelter from adverse weather (should be very good weather for you in January).
The Clippers are a place to relax. The daily programme will be delivered to your cabin the previous afternoon / evening. Drink prices in the bar and the restaurant are reasonable. It is often said that you meet very interesting people on the Clippers - we have and we are still in touch / friends with some of them
Have a great time