Re: #2 - I think it was a combination of luck and stubborness/determination born of financial and personal necessity, but I didn't change my schedule or anything right up until the day my baby was born. I worked throughout the third trimester, and while generally my job was an indoor desk job, for the last 3 weeks or so before my baby was born, we ran an outdoor theatre festival and I was on my feet for hours a day in July heat and humidity - and I survived. I also did an opera at about 7 months where I was constantly on my feet. People I worked with were very helpful in trying to get me to take breaks and so on, and I am sure that that will happen for you, too. I worked until the day I went into labour, and baby was fine. I personally don't think you should ask for a job modification unless there are health reasons and it is recommended by your doctor - but that's just me.
If you do decide that you need accomodations at work, I don't think you need to bring it up for at least a couple more months.
Get used to me. Black, confident, cocky; my name, not yours; my religion, not yours; my goals, my own; get used to me. -Muhammad Ali