My 2 cents for 1 and 3
You don't NEED to create items to order on the PO...BUT items help keep track of things...If a year from now you need to know how many of Model X you ordered, or what you paid a year ago, if you are relying on users keying in the descriptions you are going to have lots of inconsistent entries. Items also help drive the charge account...you can link the account to the item and users don't have to worry about entering in the distribution every time they order.
From what I remember with FA, whatever you put for the item description on the invoice is what comes into FA for the asset description
How are you going to be receiving and billed for the solution (assuming a 3-way match)? Enter your PO based on how you will be billed/want to pay....ie if you are going to be billed incrementally for the services, have that as a separate line with your hours as the quantity and 1 for the price. Then you can receive/invoice based on your hours as they are performed. This way you can still receive/pay for the Hardware separately and if for any reason you are unhappy with part of the service that can be tracked separately and payment withheld while you are working it out or vice versa.
hth...just thinking of some of pain points we've worked with over the years