What is the best setup for this use case?

Question 1:
I want to have founding members, for whom I want to give full 100% discount on the first year, but get them to checkout so they are subscribed for renewal after the first year. They would be subscribed at a 50% founding members price.
Then I want other founding members (who arrive a bit later) to benefit that 50%, and later full price members.

Should I create 2 products? founding and normal members? or same product where I change the price? Will the original ones be renewed at the 50% price even if I change the price of the product? Or should I use coupons, but then is the renewal at the same price (for those who are subscribed to 50%?)

Question 2:
I need to be able to manually change the renewal date, as my members will get additional months of membership as a perk for them doing some tasks (contribute content, translations or hosting events). How does that work with the date or renewal?

Question 3:
I tested Manual payment (selected "Pay with cash upon delivery"), but it doesn't work with subscription. How to do that, so they are subscribed (and get access to members area) and their subscription ends if they don't pay (manually) for renewal/where I would manually add the payment.
It's important to me as I need to be able to receive other means of payment that are not available or automated, such as bank wire, Twint (in Switzerland), or even why not crypto.
An idea would be to give them a coupon once they have paid? I welcome ideas.

Question 4:
I will have sites on a multisite network, as I need one site per language. It's way easier (for all stuff: community portal, courses, FluentCRM campaigns, even simple emails that goes with everything). For an easy process and statistical reasons, it's ok if they buy their membership in English on the main site but then I need to make them access Fluent community portals on other subsites (other languages). I'm trying to think to the best approach and automation, and I welcome all comments or ideas

Thanks a lot Shahjahan Jewel and the whole team, and thanks in advance anyone for your comments ❤️