If you add standard movement to bases simply take away the tactical movement. I am pretty sure you should be able to set it up so that you can have a standard engine or a tactical engine but not both.
If you are concerned about killer starbases roaming about wiping out fleets and planets, you could even make the engine that moves them in strategic have some horrendous combat penalties or whetever. Then you can move the base where you want it, and them retrofit it to remove the strategic engine and replace it with a tactical engine when it reaches it's post. If it got pounced on while being moved, oh well.
Of course you could load up the base wth missles and stuff that are not affected by combat penalties, and religious races would still be allright with their tailsman, so maybe I am thinking too much.
Yes the maint reduction comp would stack with the hull maint reduction. And it would stack with other maint reduction comps, so you want to make sure you limit the number per hull. And make sure the max maint reduction comp and the max hull maint reduction don't equal more than 100% or your ships starts producing resources out of the vacuum.
Geoschmo