What cost should I budget for e.g. real estate contracts, closing agency (title company)?

I pay attention to local news, become familiar with local employers and government agencies.

See if any of the local colleges or social service agencies have any programs that you can promote or even pay someone $100 to come teach a few classes. 

For example, if I want to sell a five-unit multifamily in Washington DC, it seems these agencies will market almost exclusively to their own clients -- and thus end up on both sides of the deal (dual agency). 

And from there, any suggestions as to which agency to approach for training?  

They are probably listed on the Oregon Real Estate Agency website (the state board the governs real estate agents).  

(U) "Exclusive right to sell or lease listing agreement" means an agency agreement between a seller and broker that meets the requirements of section 4735.55 of the Revised Code and does both of the following:(1) Grants the broker the exclusive right to represent the seller in the sale or lease of the seller's property;(2) Provides the broker will be compensated if the broker, the seller, or any other person or entity produces a purchaser or tenant in accordance with the terms specified in the listing agreement or if the property is sold or leased during the term of the listing agreement to anyone other than to specifically exempted persons or entities.

It is best to establish a relationship with an agency you trust and then work with them on your individual properties. 

Contribute full 3-5% and transfer to mission agency when we get onto our career placing (agency we are going with pays salary and could roll into an IRA)2.

@Tim Ellis We have had two attorneys and even had our insurance agency to contact the underwriters as well and nobody will give a clear cut answer to the issue.