If a pram you're looking at says it can take any Maxi Cosi seat then the Pebble S will work as well. As others said the vast majority of prams on the market are compatible with Maxi Cosi.
Car seats aren't totally flat, so while they are essential for use in a car, it's best to try and minimise use outside of a car, especially in the first ~4 weeks. It's up to you what approach you take to do this - I like the time limit approach which is to have a rough idea of when you put the baby in the car seat and imagine a timer counting down, up to 30 mins in the first four weeks, up to 2 hours after that. And try to either end the car seat session by that time or take baby out and give them a bit of a break and a cuddle. TBH, they often want a feed or change after a couple of hours anyway, so it's not a huge problem to do this.
Some of the advice says you should take them out of the seat and lie them flat as soon as you get home, but I never really did this unless we had been driving late and it was pretty much their bedtime, then I would try to transfer them to bed. If it was just a nap, and we were still within the time limit, I'd let them finish the nap as long as it didn't push them too far over. And keep the car seat in view and keep them strapped in so I could see they weren't falling into a dangerous position where their chin is pushed onto their chest (put your own chin on your chest, and see how this affects breathing).
I didn't use the car seat as a rocker or chair in the house unless we were about to go out and I wanted to get them settled in the seat so we could get everyone else ready (and in this case I started the "timer" in my head) or sometimes when we were on holiday or visiting someone for the day and they didn't have anywhere else to put the baby, but a blanket on the floor or even just putting them straight onto a clean floor is also fine, and good for them to have the option to roll around and stretch their arms and legs without being restrained by straps.
The inserts in the Maxi Cosi Pebble seats are usually good for baby positioning, so don't worry too much, do be a bit more cautious in the first few weeks, but you won't want to go out that much at that point anyway as you'll be sleeping very little and establishing feeding. Don't overthink it :)