No problem with the eight if they're comfortable sharing 4 cabins. A 45' cat with four heads (not 2) also makes it a bit more comfortable for newbies, but that's minor. I expect you have experience, but the main thing to consider is whether your crew of six newbies will be calm and helpful. Consider how much you're putting on yourself to keep everyone entertained and, more importantly, safe. I've taken my crew out on test sails at home before making the trip just to be sure they have the basics down before we get on the charter boat. But the boat itself is built for that many people+.

I've found that I also like the spring and early-summer months. Wind is still great and there is a bit more light in the day. Have fun!