@Kidneycutter you don't make it clear if you are looking to make 2 separate doors or a "french door", or what material you are using and are they to be painted, is the 45mm stock finished size or sawn, and are you making a frame/s as well.
In any case your starting point is your stock size, most external doors are 44mm thick, (I generally make all mine 58mm.)
You could get a 20mm DG unit in a 44mm but it does make your upstand and beads thin, 16mm units would be a better size, if you fit it with security or butyl tape you need to allow a couple of extra mm for its own self thickness, or you could use a full silicone bed (make sure its suitable for glazing) I wouldn't bead internally unless you can allow for draining the rebates, or its a sheltered position, and if you do you, will need to cap and seal the external upstand to mitigate water getting in.
I would suggest you don't cheap out on materials for the sake of it, look at Tricoya for a panel material.
Beads on the outside would be a security issue as they could be easily prized out and allow the glass to be removed
I wouldn't say it's ever easy to get a glass unit out of a wooden door or window, unless you've got a couple of hours to do it.
