Let me make a suggestion you didn't ask for. I do not do work for individuals but have been a commercial photographer for almost forty six years doing only corporate work.
If you're going to start working for pay get a business license and set yourself up as an official business. Ok you might say I'm not going to do much work but think of it this way. If you set up a business you collect taxes for your city, county and state which goes into the school system, the roads, police, libraries and etc. The money you collect helps provide funds for education and to support the community. As a professional I see too many "photographers" operating out of the trunk of their car and working without collecting and paying taxes back into the community. This hurts your kids education and other services you want and depend on. Not only the above but it's hardly fair to the professionals that have dedicated their lives to the industry, doing it legal and depend on the income to support their families. The playing field should be level in my opinion. The net result of part time "pros" without licenses and paying taxes and working for pennies has resulted in the death of a once great industry by ten thousand cuts.
Do the community, your kids and the profession a favor and get a license and collect and pay the taxes due to the community. Price your work relative to the market not under cut everyone and think you're making a killing. this is one of the biggest mistakes a startup can make. You my think you're making a killing at $35/hr but most likely you're losing money. When you're in business every penny that goes into getting you to the job and back, a portion of your utilities, equipment purchased, repairs, insurance on gear, depreciation and wear on your car, tires, your tax preparer and etc are all part of the cost of doing business. You say I have the gear or I have to pay insurance anyway but it's still part of the cost of doing business and you'll need additional gear, repairs, and other unseen costs.
Also consider if you get caught by the state tax folks you're in deep you know what. My ex assistant got caught because he invoiced a client and didn't charge tax and the client was audited by the state tax folks. the came direct to my friend and let me tell you it was thousands of dollars in interest and penalties. I know several other designers and photographers that have been caught and it cost them in the five digits to settle and in each case the taxes not collected were under a thousand dollars. Times are so tight in the industry in my state that the professional organizations have launched a campaign to turn these folks int the state revenue department and are doing so. Your chances of getting caught are quite high now and it's not worth the risk IMO.
As to your question, I do shoot executive portraits for a couple of clients. I have shot with my M9 but really found it unsuitable in my opinion. I much prefer my Nikon D800 or Hasselblad digital. Framing is too inaccurate with the M cameras and seeing precise framing and a larger image in the VF is a real advantage. 10MP will be a big disadvantage too if you get an order for a large print. Also I find rendition of the M9 for portraits to be less pleasing then the CMOS of the Nikon, YMMV. The CCD in the Hasselblad renders skin much nicer than either. I might note too that I custom profile each camera for each lighting condition.
Hope you don't take offense but this is just my take as a long time pro that's seen the decay of the industry by exactly what you're about to do. Do it legal or don't do it.