what is the best way to plant the MC? Spray soil, plant, then fill?
Yes
You can also plant with completely dry soil - Jurijs mit JS uses this method (you'll also see George Farmer doing so in recent videos) just misting occasionally
Green Aqua sprays soil just until damp, then begins planting, occasionally misting (again check their videos)
Planting always begins in the shallow substrate areas, as these can become flooded as planting progresses (more an issue in larger tanks)
In the various videos, notice how deeply the 1-2-Grow type plants are inserted into the soil
Also the planting of separate small bunches vs larger clumps improves "lift off" - after flooding it's typical to see loads of fine bubbles on the plant leaves, this gives quite a bit of "lift" (why stuff is floating in the morning after
😉)
I would not flood the tank, then remove as much water as possible - I find the above methods much easier/cleaner with fewer plant floaters thereafter (the dry or damp soil settles in about the plantlet much more firmly/closely)
Note if you have current directly hitting any substrate areas, this will lift/tumble soil & release plants
Most plants are very susceptible to "lift" for the first week or two after planting, so I don't substrate vacuum even close during this time