Hi again Ninja
I am in Bavaria, between Munich and Nuremberg, but closer to Munich, and have kids of 8, 6 and 3. I'll try to answer some questions.
If you don't plan to work it is in your interest to get married as this will mean your DH will be in a lower tax class and you and the kids can be on his health insurance. However if you plan to work I am not sure there is any advantage, and in fact you may be short term better off tax wise unmarried (though when you do your tax return it would even out I think - hazy grasp of the complexities of hypothetical situations).
We have been here 7 years - I kept my UK bank act on my German address like Nutella - but you need a German one too or else you will be paying for everything in cash - even supermarkets don't take credit cards nor UK debit cards, you need an EC card which is a debit card for a German bank account. Also of course you would be paying to exchange money all the time - so open a German account once you are here.
Cost of living is "how long is a piece of string" - if you are moving from Newcastle it will be more expensive in Bavaria, if you are moving from London it will be cheaper. It depends where you shop and whether you run a car, and most importantly where you live - city centres can be very, very expensive, but there is less of a commuter belt, so if you move out of the city you get more for your money much closer to the city than you would in S.E England. Food costs are broadly the same as in the UK. Child care is cheaper, but less available, I would say, but again there is a choice of state and private - state places are subsidised and usually at least as good as private or even better (unless you want a specific approach - if you want Bilingual you need to go private, but then if you aim to stay long term I wouldn't recommend bilingual as many kids then stick to their strongest language).
I see you are thinking of private school, so that gets around the awkwardness of moving with a 6 year old who doesn't speak German but would be due to start school! Assuming the one you mention is English medium or bilingual?
Far more mothers work part time than full time and many mothers of an under 3 don't work here - Bavaria is very traditional, but big cities are "ahead" (if you see it that way) in terms of both parents working and more childcare being available. Thare have been changes in the law recently entitling children between 1 and 3 to childcare (Krippe is nursery, Tagesmütter are childminders, you also get "Kita" in cities which are combined Krippe (under 3 year olds) and Kindergarten (3-6 year olds). However in Bavaria there simply aren't enough places in existence, so childcare for under 3s can be scarce in some areas, and in some cities the chances of getting a state Krippe place if you are not highest priority (working single parent or sibling of a child already there) and have not applied already are very low. However you will probably find a Tagesmutter or (more expensive) private KiGa place if you do want to work, and they are also more willing to be flexible (a lot of state Krippe insist children do core hours, meaning they have to go every morning, with afternoons being optional). Once your youngest is 3 there are far more Kindergarten places than Krippe places.
Not sure if that's any use. Is the job definite? Is it fixed term or for the foreseeable future?