Dedicated Authoritative server

So i've been researching this for a few weeks to determine what course of action I need to take for my game.

I'm going to be having micro transactions with some consumables and some non consumables. Then I need to store this persistent data. Originally (before the plan to have IAP's) we were intending to use steams P2P system t handle networking and matchmaking. But using the host as the server obviously opens up the huge security risk.

This game is going to be competitive multiplayer, as such needs to be authoritative to minimize cheating. My research implies that dedicated is definitely necessary, especially for IAPS.

I've seen A LOT of seemingly contradictory posts. I'm trying to piece things together but i'd like to try get some affirmative answers on a few things:

1) Can I build an authoritative, dedicated server using unity's inbuilt networking code, for use with Unity services servers?

2) Do I need a separate database to store players persistent inventory, or does unity service include such a thing?

3) Is any one able to point me in the direction of information on how to use an authoritative server to interact with some form of database in order to have IAP's calculated on the server and handed directly to database, so that the client never actually interacts with them - simply requests the use of those stored.

4) Currently my choices seem to be between PUN and Unet for what I want to do, but I've seen posts about photon not being able to handle Unity physics etc. Given my requirements, can any one provide advice on what would be better suited?

I would greatly appreciate any help in any of these areas. Networking is new to me and I'm keen to expand my knowledge of it. But most information I can find simply states "don't trust the client" which is obvious, or tutorials on how to get IAP's working in your game, rather than how to securely implement them.