Many of my big mistakes in past years were from too much concentration.

I personally detest door count and concentrate on up front profit and long term.

It can allow you to filter out some of the ridiculously overpriced investment properties you're seeing listed, and can allow you to concentrate more on the ones that deserve your time. 

In fact investor concentrations will increase as you work your way downward on that scale.

I would concentrate on notes if I was you.

You will own the property for many years, so you will need several reliable tenants.To have reliable tenants, purchase a property that attracts a tenant segment with a high concentration of reliable people, and work with a property manager with the skills to select reliable tenants.You can identify such a segment through property manager interviews.

That’s atop the already complicit role Airbnb continues to play in protecting illegal subletting.There’s a place for STR in any area, but the overcrowding of O’ahu atop the high kind of concentration of STRs in small areas can rapidly turn tourist cities into a dark, transient, ghost town if left entirely unchecked.

The floor is built to handle 40 pounds per sq ft (I believe it takes 300 lbs concentrated).

The Western Pennsylvania region's concentration of colleges and universities is a positive indicator for sustained demand in this niche market.

Here are the areas to concentrate on:LEAD GENERATIONBandit SignsCold calling     Probates     NOD’sDirect Mail (Very expensive and I don't waste my time or money on this)     Any listDoor Knocking     NOD’s (Least expensive way to directly speak with someone who you know is in trouble.)WebsitesFacebook/Google Ads (This is where I get the most bang for my buck.)Hope this helps.Good Investing...