I have a friend that told me it’s illegal to own a townhouse and rent it out because the location of the property is in a median income area.

It's fairly common for parties to include only a property address in the contract... when what they need to do is provide all Tax IDs associated with the transaction.

Being on a team is personal preference, but I prefer it because I like the camaraderie, support, and accountability of a team. eXp Realty also allows you to make your full commission on a couple of your own deals per year (minus a few minor fees for the transaction), which I find very helpful in general and as a real estate investor. 

Looking for someone to manage my business & personal taxes / real estate transactions.

Sounds pretty creepy, and probably illegal.

I am an agent here in the Seattle area, and I have 17 transactions in the first half of the year.

It's a process that includes both the research of risk in a transaction, and finalizing the acceptance of that risk. 

I would recommend attending some training sessions organized by the local realtor association with which you plan to align yourself with to help network with the local agents and familiarize yourself with the local loan officers in the area (these events are usually sponsored by the local lender branches) and the start to finish process in the RE transaction.

If you owned the property before the transaction, and will own it afterwards, it's not a purchase mortgage.

Why would you want to do your first transaction off-market and without someone helping you?