Can I get a singular bonus in there at a specific level (like a movement point or another ability) by using ?
That's kinda tricky, short answer is no. I could be wrong on this but....
If you look in CoreMonsters.xml, you'll see there are different stats specified for different levels. You can make interesting increments there, like give a UnitType an extra move point at level 10.... but it won't automatically happen when they reach level 10. Those stats for the levels are the attributes a monster gets when they spawn, either via goodie huts or a summons. But if a monster is spawned at level 1, and gains another 9 level to 10, they don't then get the stats of a level 10 of the same type... instead they level like a trained unit, +1 accuracy and spell resistance and +2 hit points per level (or whatever it is, something like that).
Weapons can have a level as a prereq, checkout Staff_Winters for example.
I don't think that that will work on a ability that you give to a monster though, like if you create a +1 Move ability that has that prereq... then give it to a unit... it will get +1 straight away. You could test it yourself though, I might be mistaken.
I think the level prereq will work for a Spell though, or a Spell like ability. So if you gave a unit an ability that unlocked a spell like ability (like Maul for example)... if you put a unit level prereq on the Maul spell that might make it available only when the unit reaches that level. I think that works.
But the specific things you mentioned, won't work as far as I know.
I have another related question. Can I auto upgrade a unit type when it reaches a specific level, e.g. upgrade a bear cup to a bear at say level 5?
BTW in case you weren't aware you can use fractions, so you could have an ability that gives 0.1 move every level... that would be rounded, and give +1 move at about level 6 I think.