I am a contractor so I got started with a mechanics lien and well the cash flow was nice.

that's great to hear you have an interest in real estate - I got a degree in Mechanical Engineering - i was really good in design / math - but just hated the type of work..

Or the house need a new round of roof, mechanics, electric?

You get what you pay for and a good Agent is like any other trade. would you pay a flat rate or very cheap Dr or mechanic.

The owner had passed away so its not like anyone had an emotional connection to the house.Surprisingly the house was in good cosmetic condition considering it was vacant but all the mechanicals were old. 

I work as a mechanical engineer for a consulting firm in the Baltimore area, but my passion has always been for running.

Also as Steve B. said they are most likely 100+ years old with original mechanicals (HVAC/Electric) which can be very costly to replace.So what do you guys think is it better to aim for $150-$200 monthly cash flow per door or a Cash-on-Cash return of >10%?  

I am involved in construction sales & operations on a daily basis and have a high level of understanding on how the business operates, specifically the mechanical aspect (my specialty).

My advice is that the mechanics of of doing the calculations are rather straight forward.  

Lis pendens is that SOMETHING is holding it up and about to be recorded... until you know what that is you don't know how to get rid of it (that is why they suck).. it could be a mechanic's lien or a tax lien or a fraudulent quit claim deed... all have different ways of being removed.The best way is to be able to prove it is fraudulent...