But high level:1) If the units rental income doesn't cover mortgage its not going into my buy/hold portfolio , I have a separate "appreciation" portfolio for that on (think San Francisco where CAP rates are 3-4 , but if you can wait out or turn low rent controlled tenants you can improve the building profile.) 2) I am currently looking for places in B- to A- areas.

There are certainly no guarantees you won't get a bad tenant, but I wouldn't completely rule out an area because of the current laws.

My agent has the ARV comped out at about the same, and maybe even up to 175k with higher end improvements.

Sometimes you want to improve your credit score needing some time to get it up there.

I did property management in CA (years back) and I remember there was no rules or regulations.

It is ordinary and necessary for real estate investors to notice wear and tear from year to year and claim "depreciation" on their properties.The rule that your accountant is referencing to is the "real estate professional status" which allows you net losses from your rental activities with your other income if your adjusted gross income is above $150,000.

My question is, are there any rules preventing me from working exclusively with investors?

Legal Fees $2400 Deposit Required for the mortgage - 20% - $35,000Right now rehab - 22,000Property improvements and correction of deferred maintenance over the next 2 years - additional $24,000 Mortgage payment - 871$ / monthWater - app $200/monthProperty Tax - app. $300/monthGrass/snow - quoted by a local company at $274/month (1800 for snow for the year, 1500 for grass for the year) Insurance - $140/month (got a great rate not cheap insurance) The heat source and hot water is natural gas, New furnaces and water heaters installed in 2015. 

Yet I keep hearing about this 50% rule that half the gross rent will be put towards expenses... is this rule really applicable to Boston?

Building new, rehabbing, buying tax deeds, ect etc...I like them because they are setting the comps in local neighborhoods that need improving but I would like to see how thier business model survives without such a strong market.