Sounds like you have a bunch of worries. Ease your mind. If she nurses to sleep...who cares. I did it too, even though other moms think it's Taboo, she won't be going to college like that so do what feels comfortable for you and what works.
The carseat thing, my daughter always fell asleep in it and sometimes, it was the only way to get her to nap, so naptime...we went for a car ride. Oh well...taboo again I guess.
As far as a routine...this is what I did. At 3 months, they still need alot of sleep, but at around 4-5 mo's, she can probably go to 2 naps a day. I'd shoot for 10 am and again at 2 pm. Get dressed in the am when you wake up and eat breakfast, then play and read, etc. Nap at 10 am. wake up and do lunch. After the 1st nap, we would eat lunch, and then play, cuddle, go for a walk, etc. Then, it was soon time for a 2nd nap. I always did my outings after the 2nd nap. More play, reading, errands, outside time, etc. Then, fixing supper for you and downtime, or individual play. When I was fixing supper, this was my daughters time to sit and watch sesame street, or a short video. Also, many people experience a bad mood from their kids at supper time because the child didn't get any wind down time, and this elimimnated her supper time temper tantrums. Then, eat supper, play, bath, reading, bedtime. Of course fit in the nursing whenever you want...depending on your schedule. Hope this helps with a basic outline. This worked great for us and we are now on a single nap right after lunchtime. Good luck.