There is no need for an Immigration lawyer, it would be a waste of money, (if they even exist here, I've never heard of specialist Immigration lawyers, the only time you might need one is of you were in dispute with the Immigration Department and that is only likely to occur in a residence or citizenship situation and even then I've never heard of specialist immigration lawyers being involved). Unless you are in dispute a lawyer would add no value.
The options are straightforward:
a single trip visa, with a three months extension, leave for two or three weeks and repeat, I know people who have done this without problem for three or four years;
or residence in the form of Class K.
"Residence permit issued to persons who have an assured income derived from sources outside and undertakes not to accept paid employment of any kind.
Class K Requirements.
â—¦Documentary proof of assured income is required for Class K.
â—¦Processing Fee Kshs.10,000 non-refundable.
â—¦Fee is Kshs. 100,000/= per year or part thereof. "
More info here
There are people, especially here at the Coast, who stay here without residency and the Foreigner Certificate, (the iD card) and don't have PINs, etc some own a house and / or car but they have to be in their Kenyan girlfriend / boyfriend or wife / husband's name and as a result things often end badly for them.
If you want to try living here why not come, get a visa then extend it, the six months will give you plenty of time to find out if you want to stay and how things work, and whether you need anything that requires an ID number or a PIN, etc. Personally I think if you are going to live in a country you should abide by its laws and rules, I try and do everything by the book (which often isn't easy in Kenya, it would sometimes be easier not to) but there are expats who bend the rules or live outside them and they are fine until something goes wrong or they have a problem. As long as you took a holiday for 2 or 3 weeks every 6 months you should be ok coming and going for a couple of years at least before you were unlucky to join the wrong queue at the airport and find a zealous immigration Officer who might think you should be applying for residence, and that surely would be enough time for you to decide if you want to stay here long term, and if you do that you might want to integrate more fully and to do that you would need the things that come with residence.