How many impedimenta is avaiable per scenario ? I guess this number is fixed per the one we start with + we can recruit ?
The number varies by scenario and force pools are adjustable in the Game Options. I believe that this also applies to impedimenta.
How long does it take, after we use a wagon to build depot to be avaiable again for recruitment ?
In my experience, next turn.
If we will lose impedimenta in combat, will we be able to recruit it again ?
You should, except see below.
Also for the winning side, this supply wagon is just the extra one they have above their limit, and if they would build a depot from it, it won't be avaible for repurchase ?
Pretty certain that captured impedimenta do not increase the allowable number. Therefore if you're at the maximum allowed and capture two, you need to lose or expend three before you can purchase a new one in the Build mode.
-C