If you copy only main movie - it is not much where you can save quality wise. Strip unnecessary audio/sub streams (shrink can do this), cut off studio intro/creadits (better to use DRM as it will let you convert video to still while keeping intro/credits audio), strip angles you don't need, if any (don't think Shrink does this).
But actually when you will master DRMP you will probably stop doing movie only backups and will include menus as well. Since they will not take much space (can be converted to still) and will allow more comfortable navigation to chapters (at least).
Combining DVDs is really simple with DvdReMake. You've probably already seen guides on this at DimadSoft.com
All the minor versions (3.X.Y) are free for registerd users of DvdReMake Pro 3. Upgrade to next major release (v4) may cost something, but registered users will not pay more than 40% of v4 cost to upgrade. There is no plans to release v4 anytime soon (not within next 6 months for sure).