You're very welcome!
1) will the cycle be instant or still take a few weeks ?
I am of the belief that no cycle is instant. Though with mature substrate and filter from other healthy aquariums, it should be sped up. Every tank is unique, ultimately your test kits will be your guide.
2)would you suggest heavily planting from the start or letting it cycle first ?
It's never too soon to plant, IMO. That will also help speed up your cycle, both from bacteria on the plants themselves as well as the plants constant uptake of nitrogen. If plants are fast growing, it's as close to "instantly cycled" as you can get.
3) Would you mix the new and old aqua soil together or layer the old on bottom and new on top? or vice versa ? or it doesnt matter? lol
Shouldn't matter much either way but I'd be hesitant to bury the old stuff simply to keep good O2 levels on the beneficial bacteria that is on it.