Hi 

So I will soon place an order but I would like to know beforehand what kind of glue I will need to stick the 6mm miniatures to their bases. As they are metal, I am thinking of buying a super glue, specifically Gorilla glue, but I do not know which one would be the best option. Could you help ?

White vinilic glue works just fine. The wide base of the miniauture strip / horse, combined with their light weight, make it more then sufficient. Also the artillery sticks perfectly with white glue.

I also use regular white glue for gravel and flocking. 

I keep super glue only for emergency repairs, when a figure snaps of the base.

Yes, absolutely only use basic white glue for everything and base on MDF. Should you ever have to remount your figures (hopefully not) just sit them in a shallow pan of water for a few hours and they just pop off. Only use super glue for repairs.