Personally I would get 1 Savi (the custom saber, probably nature), a selection of additional kyber crystals, both holocrons, and 1 legacy saber. I've watched a lot of videos on the Savi sabers, kyber crystals and holocrons over the weekend, and I think they are all worth the cost. Great value as collectibles and cosplay/roleplay props. Personally I think going to Galaxy's Edge with buying a lightsaber or two in mind and NOT getting a Savi saber is a mistake. They have more features and have a uniqueness to them. Also as you stated, the possibility for custom third party parts down the road might be interesting.
I'm waiting on more reviews and impressions on the legacy sabers. When I first saw that the RotJ Luke saber had two top sections (thin neck and fat neck) I was turned off, but I think it's bothering me less now. Afterall, you would probably display it unignited with the thin neck attached 99% of the time, so it shouldn't be make or break. You'd only see the thick neck piece on rare occasions when toying around with the blade.
I really want to see someone review the Rey saber an compare it to some other graflex sabers in this price range to see how it stacks up. Most importantly, is it identical to the previous Disney Parks exclusive Rey saber, or have there been improvements made?