My Girlfriend and I had a very similar situation last year.
We both completed several courses with Offshore as well, at their Captiva Island office.
We did our first Charter with the Moorings out of the BVI last April. We picked a Bene 35 Club as our boat, but out of either a hidden policy or just sheer luck were upgraded to an Exclusive 39' when we arrived, free of charge. We were absolutely ecstatic to say the least. I will also say that the condition of both Club and Exclusive is night and day. Its worth the upgrade.
Of course that meant that we had to handle a 39'er ourselves but we did great.
My advice up front would be to make sure to do a very thorough walk-through before you set off. Is there an inverter onboard etc etc. If you still have the Offshore Checklist that they used in the classes I would definitely suggest using that as a guideline or just reading up on common problems with the boat you plan on choosing.
Lastly, make sure to cite as clearly as possible in your sailing resume your Offshore courses in detail as I think that helped a lot with how the staff received us when we arrived. Last tip is to use a cruising guide other than what they provide. We found many people using the exact sail plan as described and found many hidden spots too late.
Feel free to IM me if you want any more insight for a first timer charterer in your position.