You are going to love it!!! Take every day you can.
I just started a new job for a company HQ’ed outside Grenoble last October (I’m based in US) and will be making 4th trip over in June and can’t wait! Instead of renting, I finally plan to fly bike over this time as well.
Bourg d’Oisans is a fantastic base to ride out of and I’d suggest just get a Air BnB in that general region on wkds. Traffic crossing through Grenoble can be soul crushing - I hear Lyon is worse. It’s not a round trip you’d want to do daily. Gite de la Lignarre in Ornon (a few mins from Bourg d’Oisans) was awesome inexpensive place to stay for a weekend and cyclist friendly. My first trip I stayed in Grenoble and on weekends, driving there to Bourg d’Oisans is reasonable - but still, unnecessary when there is ample cheap accommodation in Oisans. (SO many out-of-season ski apartments)
Alpe d’Huez is sort of compulsory, but it’ll be the least scenic climb of anything you ride there. I have a bunch of rides on my Strava with photos - pasted a few below from October. Was back in Dec for another day of riding - weather was crazy but still cool. Croix de Fer was fantastic; there is a balcony road (D211A) that runs up over the valley that was stunning (see Dec pics where I rode through and over the clouds), a much less traveled climb is up to the remote village Oulles that only got a road in the 1960s I think and hardly has any vehicles on it; Valle du Ferrand (sp?) which connects to Col de Sarenne was also great. I’d also recommend riding out to La Berarde - particularly low traffic and remote. There is a good free guide book for the region that lays out many of these rides and the major climbs all have cycling-specific markers every km.
Lots of photos and some ride ideas:
From Grenoble area, there are also many good options and it’s very easy to go between Grenoble-Lyon by bus or train. It’s really hard to go wrong from what I’ve seen so far - I haven’t been to Lyon to say for that area. The Chartreuse mountains north/NE of Grenoble were beautiful.
Another option you might consider is Vercors. There are some absolutely stunning roads that wind up the canyon walls - has a different feel from the Alps but still incredible. My only concern there is that cyclists were not as widespread in October and the roads had a bit more cars - but I’m guessing there are plenty of cyclists in season. I’d be interested to hear from any other locals or travelers on how it is riding those areas.
I also checked out Annecy one afternoon in February - it looked much more developed and the mountains were a bit “softer” than the Oisans region, so I’m planning to spend more time in Oisans again on my next trip - still much to explore. And I’d like to get up the Alpe < 1 hr just because… need to knock off 3 minutes. Every little village has public water springs too - I carried two bottles up the Alpe totally unnecessary - I’m hoping that gets me one of those minutes next time 
Better training, having my bike + power meter to pace, and not doing it jet lagged < 24 hours after landing on my first ever trip in France should make it achievable! But seriously, it’s the least scenic ride of anything I did there - it’s just a nice test with minimum distraction on the way up.