I got married in San Louis Obispo I think it's called, in a little gazeebo by the ocean. (11 family members in attendance) I got my dress at Walmart of all places - a nice little white cotton dress like you mentioned. My husband and I both wore all white. My white dress and white sandals, his white cargo shorts (Macy's, Dillards, one of those) and white button up short sleeved shirt and white flip flops (Old Navy). I can email you a picture if you want one - just PM me with your email address. We did a lot of shopping to find exactly what he wanted. (We got married in August, so no had no worries about coolness. I actually got sunburned in the 1 hour we were hanging out there).
I think tan dressy shorts would look fine if your man finds a white shirt to go with it. As for sandals -- well he'll either have to get over it, or maybe he should do white/tan pants and wear some sort of brown/tan shoe/loafer. If you search for ideas for him, do a google search like "Hawaiian beach clothes" and a few ideas will come up.
Good luck. Not sure about the shawls. Sorry.