It is possible to include contracts as lessor as well in ZenTreasury.
1. You create contracts normally as you did before, but now you put your "payments" as negative value, because you will receive those in the future.
2. IFRS - tab :Not active
3. You should make your own portfolio / lease type for these kind of situations, so it wouldn't mess your reporting. It is up to you how you want to separate them.