In addition to a full tenant screening, you can request pay stubs, w2, etc. in the application they submit.

We didn't do it from the beginning, because we felt negotiations were easier  under my name with this particular seller, and we needed the seller to sign the contract ASAP before a higher offer was submitted. 

I am considering agreeing to this provided they submit a nonrefundable payment of $1,000 (two month's mortgage payments) right now up front to hold the property in case they end up bailing and the property goes vacant for several weeks.

The seller stated to me the asking price and requirement of me to submit a Purchase Proposal so he/she can have an idea of economics before sending me any current lease information.Just curious to know what exactly the seller is asking me to include in this Purchase Proposal...?

Many use the 1% ruleOnce you've submitted an offer and the seller accepts, Talk to a Property Inspector.

Do I have to inform the seller that I intend to use the property as a rental property when submitting a purchase offer for it? 

I would submit that finding a property that would pass that test is nearly impossible in the current environment, still I beat my head against the wall daily in attempt!

Am I able to submit offers to the sellers agent without using my agent?

In the process of making an offer (but just prior to submitting!)

. - Self managing a couple units is a great way to learn the business.Property Management Software - check out something like Cozy.co - it helps you list/market your units for rent, lets prospective tenants apply online and does background & credit checks, then once you place a tenant they can pay online along with submit maintenance requests.