Cinch Plus is selected for you at checkout, and you can remove it before you pay. Cinch Max is never pre-selected — you would need to choose it.
Whichever tier you end up with is set for the length of your contract. You cannot add, change or remove a tier part-way through, so it is worth taking a moment at checkout to choose the right one for you.
Your entitlement start date is the day your subscription starts. There is nothing to wait for.