What are routine (monthly, quarterly, yearly) maintenance stuff I should do to make sure my rental is in good working order.

If not and the property has foreseeable maintenance SELL. 

My goal is to get the Max rents and limit the maintenance.1.

#4 Talk hubby into it if the future cash flow numbers are solid and there are no deferred maintenance surprises. 

If you're up for it C & D class can provide great ROI just be aware that there's more risk involved ie generally worse tenants, less desirable location (Higher vacancy), higher maintenance costs, etc. it's all about what you're after low risk or high roi... 

You should check with a title attorney to be sure as laws are always subject to change, however, I believe this first right of refusal only applies to Baltimore City, not the County: Under Code §6-1, before title to any single-family residential rental property is voluntarily transferred, the tenant of that property shall have the opportunity to purchase the property on terms considered reasonable in the residential real estate market.I would advise him to give the tenants notice, move them out, take care of deferred maintenance, paint/carpet and sell the properties vacant.

@Brian Lewis technically 90% of a property manager tasks can be done remotely (rent collection, maintenance request, bookkeeping...)

However exterior maintenance is treated like a SFH.

You as the operating partner are responsible for the management of the property: finding tenants, maintenance, overseeing and organizing the financials, etc.

This does not include the money you will spend on repairs and maintenance for normal repairs.