I say just don't rush anything. Everyone at this stage is likely caught tightly in the NRE web. Damn it all feels so right
Let it mature for awhile. I think there is a 'trick' to keeping the balance right on contacts and time together. As you wisely considered, too much can be annoying (needy? etc), too little my give the impression it's fading or not that interesting long term. So you want to reinforce that you find the whole model - AND THEM - very much to your liking and way of thinking. Once they understand you are sincere in this it should be easier to navigate.
Of course you have to be watching for the same thing from them. SO many people have the fantasy of 3 way relationships that when it seems they have stumbled into one the get all giddy. It's NOT going to be all fun & playtime in the long run. There's some tests yet that you all have to pass.
Be patient, be prepared