Coupon/Subscription/Level CONFUSION

I'm attracting 3 groups of people. Normal Members pay $69.95 per month.
Group 1 are former members of a closed company, whom I have the list of them (all 22,000). I'm offering them $19.95 per month for first 3 months, then back to $69.95. My thought was to email them today with a Coupon Code.
Group 2 are members of another company I own who I'd like to give them $19.95 forever. Also thought a Coupon best for them?
Group 3 are normal people joining who pay $69.95 always.

ALSO, does the Coupon Code start and end date apply to when the Coupon no will function? (My assumption)

ALSO, the Subscription: If I set to finite and then a Period of 90 days, will they get 3 months for $19.95....or 3 months AT $19.95?