With the positive attitude you seem to have, I think you will enjoy doing whatever you decide to do with the rebuild, restoration. I've read several comments in this forum and other places about future appreciation of these classics, but when I watch what people are actually selling some real classics for, including pre-1970 BMWs, BSAs and Triumphs, yes, there is some appreciation, but it just isn't that great. A really rare model, yes, but the old everyday types, or what were everyday types, no, just a few thousand more than a more up-to date version will buy most of them. Even less in some cases.
I even wrote once on this forum, mentioning future value, but on reconsideration, think the value of a bike is that of what it means to you and forget the rest of the world. Collect because you enjoy, not because you plan to profit, otherwise it seems like a sort of phony, materialistic pursuit.
But I'd keep it at 350 cc, don't think you gain that much with more cubic capacity with Bullets, and you may lose a little in reliability.