I think your multiple charters in the BVI's qualifies you and mate to step up to SVG. Sailing distances are longer but not extreme. For example, the cruising guide indicates it's only 8 miles from Blue Lagoon to Admiralty Bay. Longest distance I see is 16 miles is from Bequi to Canaoun – not much further than going to Anegada from North Sound. I have chartered there in summer and in fall (November). I liked November because businesses were open and conditions were excellent with winds around 15 kts. I only recall one rolly anchorage and that was at Mustique. Never used more than 1 anchor anywhere. I actually experienced conditions you described in the BVI’s last May (i.e. 20-25 kts). Just make sure you know where you are and the island you’re heading for is the one where you want to go.
Although I think SVG is a logical progression for the crew, I have other thoughts about your guests. If they haven’t been sailing anywhere in the Caribbean, they will think the BVI’s are just wonderful - I think they are too. Also, if someone isn’t feeling well you can get them to land and wellness in fairly short order in the BVI’s. I would also consider the cost and hassle of just getting everyone to SVG vs. the BVI’s so I would do some research and comparison in this area.
Bottom line – I think it would be less stressful on the crew and newbie guests to go to the BVI’s – they are going to love it. I would save SVG for just the experienced crew.
Fred