The problem mentioned in "Virtuemart 2.0.26 Coupon Usage is not being Recorded" topic is not valid for Virtuemart 3.
The invitation page description is the text that appears at the beginning of the invitation page, so really just instructions/welcome for the user.
For 'Delay between invites', you would just enter 5
There is option for twitter. Facebook has made it really hard to allow points in this format. The plugin is still there, but it is unsupported. You can enable in in aworewards > aworewards > installation check
If you have more than one rule for the same scenario, only one rule will apply - the first one in the order. For example, if you create 2 rules for rewarding any customer after completing an order, the rule number 1 will be applied, without looking at the rule number 2. However, if the number one doesn't apply,say due to minimum spend amount not met, the system looks at the next rule in order.