I worked up until my first son was born (I was getting up for my morning shower before heading off to work when my water broke).
Since you free-lance, you need to find someone who can and will fill in and take over any scheduled jobs during the last month of your pregnancy if needed, and you need to okay it with the clients with whom you are contracted. Also, I suggest that you work up until the baby is born if at all possible--your income will take a nose-dive the moment you stop working, and there is no guarantee how long you will be off. Unless there are medical reasons, there is no reason to stop working early. Much better to apply that time to time with baby after he/she is born.
1) If you are healthy you shouldn't feel that walking and moving around are too much, even up to the last day; especially with a first baby. There are circumstances where this may be inaccurate (health conditions, pregnancy issues, carrying multiple babies, also have young children, etc.) but it is the norm.
2) It will depend drastically on your individual situation. I had c-sections that kept me from getting up and moving around as early as if I had had vaginal births. In general, with a vaginal birth they want you up and moving within a few hours. If you have a c-section, they may put you on a morphine drip--which requires a catheter for at least 24 hours after the morphine is stopped. This severely limits your ability to get up and move. With my 2nd birth I specifically said "NO MORPHINE" and was up and moving much sooner.
3) Standard maternity leave was 6 weeks, usually 8 weeks after a c-section. I would assume it is similar, now. However, specific conditions could extend the timing--it really depends on what your doctor prescribes.
You need to find some good books about maternity and read them thoroughly; write down as many questions as you can think of before your first OB appointment, and ask them all. Enroll in a childbirth program that starts early in pregnancy--many don;t start until the last trimester. It's really sort of silly to have a room full of 7 or 8 month pregnant ladies and be telling them about the foods they need to eat and the exercise they should be getting during their first trimester
I recommend Bradley classes as they start early in pregnancy and are strong advocates of being well-informed about all aspects of pregnancy and delivery. They do push/emphasize a prepared/natural childbirth, but more importantly they push you making informed choices, whatever those choices may be.