I do not recommend paying any upfront fees, unless it's with a large bank that typically requires a good faith deposit on larger transactions.

@Isaac Terry Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

Highly recommend (I require) collecting first month's rent prior to handing over keys.

Who do you recommend?"

I would not recommend that.

If you are serious I recommend Costar above all.  

Word of mouth recommendations always goes a long way with me.

Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

@Carl RowlesI recommend a HELOC or Heloan on your primary residence or the rental if you have enough equity in either.

Personally, I advocate for a long-term investment strategy and would recommend investing the funds, provided you are comfortable with the expected return on investment over time.