I know you posted in another thread and it got derailed a bit. Hopefully I can help with some of your questions or at least point you in the right direction.
I started my business in Virginia and used to live in the DC area. If you read my posts you will find I am not actively running my business but I stay involved in the industry as much as I can. Life took a different turn for me and I plan to return at a later date...I hope my advice is encouraging.
First you have to decide how to structure your business. Do you want to be a sole-proprietorship? Partnership? LLC? Corporation? There are pros and cons to each basic setup so I encourage you to consult a business attorney or accountant for a free consultation on the benefits of each structure. In my case I was set up as a corporation.
Check with your locality if you are required to submit your DBA (doing business as...) for your company name. I had an office space in an adjoining city and I was licensed in that city. I also had a DBA registered in the city of my residence. Each city has their own rules. Just call City Hall and ask.
I encourage you to read as many books on running a business as you can. While not every bit of advice is "one size fits all", you'll glean info that you can apply to your own situation. I highly recommend the "E-Myth" series of books. We've talked about them on this forum so you can get some feedback if you search for "E-Myth" on the boards.
Don't let people tell you that you have to have gobs of money to start. While it is not advised to start without the basics like insurance and proper supplies, you can invest as you go. Some have done it on a shoestring and others have spent significant sums of money at their startup. Do what works for you with the outcome always in mind. Set goals and stick with them.
Marketing is an essential part of your business. There are tons of ideas on how to market. The economy is constantly changing and so will your marketing techniques. I'd start with a website and business cards at a minimum. That will NOT be sufficient in the long run so always stay on top of channels in which to market.
You asked about the different types of cleaning services that you should consider...what hours do you want to work? What experience (if any) do you have in the jan-san business? What are you good at naturally? Are you a people person and outgoing?
There are some types of businesses that come with natural pitfalls. For instance, many business owners shy away from cleaning daycare centers. Others stay strictly with residential cleaning. Others won't touch residential with a ten-foot pole. The trend nowadays is focusing on foreclosure cleaning. The problem with that is you may be in an area that is saturated with foreclosure cleaning businesses but lacks in residential businesses. Find out what your local needs may be. Ask bankers if they have any problems finding foreclosure cleaning services. Ask your local doctor's office if they are happy with their cleaning services. Ask your neighbors and friends if they use a maid service and what they think of it.
Do you plan to expand and hire employees down the road? How solid is your friendship with your friend to be able to overcome differences in a business relationship? I highly recommend getting into the business with the mindset that you'll grow and need employees later.
That will give you a bit to chew on. I know there's a lot of information to read and digest. Just take it a little at a time and keep asking questions!