and wouldn't mind seeing some of the D day beaches but nothing firm yet
..These are (IMHO) a must. I have been there twice now and will go again. To do the area justice you'd need more than a few days but even just one or two days would be worth it.
I would take at least a day for the American sector and a day for the Brit,Canadian sector..possibly more...the battles in the corridor of death and the falise gap are also worth a trip....but to get the most out of those you should have a guide or at least a book.
Caen has a good selection of hotels which a re well placed, however I was on foru wheels so on a bike I'd probably go and stay in a B&B on one of the beaches....either in Arromanche or on Omaha beach where I believe there are a couple of B&B's towards the western end. Port En Bessin is also woth a look for B&b's. If you fancy a Novotel with a pool then the one at Bayeaux is pretty good and well situated for all the D Day beaches.
There is so much to see...the beaches, pegasus bridge, St. Mere Eglise, Merville battery, Battery des longues, the Cemeteries (especially at Colleville sur mere Omaha), ...all a must.
It's not flat along the coast though...around Arromance there are a few longish hills up to the cliff tops...but the view at the top is worth it.
There is a fast coastal road linking all the beaches...but there may be smaller more cycle friendly routes closer to the beaches you would be better off on...dunno..like I siad I was on four wheels last time.
I think you may find that a trip there is worth while...it's a very moving place to visit.
You may know a bit about the events of June 1944, but if not I would suggest reading up a bit about the areas you intend to visit before you get there...it's an amazing experience to stand where it all happened. Just to go there 'unprepared' is still a cool thing to do, but if you know more about it you will get more out of it.
Try to get a tide chart & visit the beaches at low tide. High tide can cover the entire beach right up to the sea wall, especailly omaha ....at low tide you get a much better impression of what it was really like that morning.