Not too long at all! Sounds perfect to me! That way you can relax and really enjoy each other and all WDW has to offer. I know that whenever we are there for less than 6 days it feels like we don't get enough sleep and we're always running to get everything in and still missing a bunch of things we want to see. It's wonderful to start planning now. I took an 8 day trip with a friend a few summers ago - we kept ourselves busy all the time, only had 1 ADR and still never made it to much of anything outside the parks. You can enjoy some pool time at the resort, maybe a couple's massage at the GF or SS spa, Jellyrolls piano bar, mini golf, lots of dining and show/entertainment options, etc. You'll have an amazing time!
Edited to add:
I forgot to answer your Q? in the title of your thread! We only took what I call a "Minnie-moon" - we spent 9ish days in WDW over our wedding - but the first 2 or 3 were a lot of still getting things ready for the big day, then the rehearsal, the wedding, then 3 days in the parks with our guests. We ended up with less than 2 days to ourselves! We're hoping to plan an 8 day Disney trip for just the two of us as a belated honeymoon.