some questions on cross polination??

[Rusty Trichome]

Q 1 ..at what stage in the female flowering do i introduce the male pollen to the female buds.....

When there are enough pistils to pollinate. Usually week 3 to 4. I only pollinate using a Q-Tip with most of the fuzzy stuff removed, or a fine paintbrush, on the underbuds. This keeps the cola virtually seed-free if done carefully. (no sneezing while pollinating, and turn off fans) One calyx holds one seed.

Q 2.. can i store this pollen in the freezer for a few weeks as the male plant is ready now..

Sure. Fridge works well too, in an airtight/watertight container. Make sure pollen is free from any other plant material, or pollen can mold.

Q 3.. has anyone any advice on whice strains would be best to cross

I'd try them all, but then again...I do have too many strains as a result of doing just that.

Make very sure to let the seeds mature before chopping the plant. This is another advantage to only pollinating the lower branches...you can chop the cola if it's ready before the seeds, and continue flowering the rest of the plant till the seeds are mature.