Mail a yellow letter or go knock on the door

This seems as if this is a bump that may have knocked you down and you are choosing to get back up.

I'm in between tenants and need to unexpectedly replace a 25' x 8' section of drywall, but just don't have the time to knock it out myself. 

When it comes down to it, as @Andrew Michael suggested, nothing beats school of hard knocks and testing different methods to see what really works for you. 

(2) Impact surfaces are required to be treated only if: (i) Paint on an impact surface is damaged or otherwise deteriorated; (ii) The damaged paint is caused by impact from a related building component (such as a door knob that knocks into a wall, or a door that knocks against its door frame); and (iii) Lead-based paint is known or presumed to be present on the impact surface.(3) Examples of building components that may contain friction or impact surfaces include the following: (i) Window systems; (ii) Doors; (iii) Stair treads and risers; (iv) Baseboards; (v) Drawers and cabinets; and (vi) Porches, decks, interior floors, and any other painted surfaces that are abraded, rubbed, or impacted.(4) Interim control treatments for friction surfaces shall eliminate friction points or treat the friction surface so that paint is not subject to abrasion.

If this is the case, the property I'm looking at can be knocked down to build an 8 family complex, making this worthwhile to pursue. 

That involves, direct mail, cold calling, knocking on doors, networking with mortgage agents, networking with realtors, etc, etc.You need a basic website to market yourself (validate you) to someone who might buy properties from you.

I would say cold calls, open houses, referrals, sphere of influence, head-knocking, family/friends, social media are the best free leads. 

Since it is an old home and some of the plaster is loose, it too needs to be knocked down and replaced with drywall.The paint on these walls may have lead based paint and dropping plaster will create dust.

The more the merrier i wanna learn everything and anything because even tho im not 100% i'm learning like for example 'im hopefully putting my first house under contract tomorrow with the help of my mentor ( Knock on wood ) but yeah if you have any blogs or anything i can read and learn everything or links to forums in bigger pockets anything can help.