Yes it is suitable from birth, but I know quite a few people here wouldn't use it from birth because the seat is still quite buckety. I used it with my 3 month old and it was fine. However I did feel the seat was very exposed (the sides are flat and open and the hood is fairly shallow) and I did add in a Bugaboo cocoon to make my LO feel more snug. I saw a tiny baby in a Zapp Xtra today and I have to say they didn't look comfy.
You can add a maxi cosi car seat - but you need to research the length of time a baby should be in a car seat - I think its 30 mins for a newborn and 2 hours for an older baby. Plus if you do consider using a car seat, then buy two chassis - one for the seat unit and one for the car seat - because if you lose the seat adaptors they cost circa £30 to replace each time and believe me they are very easy to lose!! I also recommend buying two used, nice loose Zapps / Chassis, then strip the fabrics off and buy a new Xtra seat to go on top. That way hopefully the fold mechanism will be nice and easy to do because a new Zapp can be a real piglet to put up and down.

If you dont drive, I have to say, you may be better with a more sturdy pushchair. The Zapp Xtra really is the sort of pushchair that is good for people who are very car based, need it to fold small and just nip in and out of places. The hard wheels are noisy and not that comfy to push, and if you have to walk a long way, it would not be my pushchair of choice TBH. I would have a think about where you go, and also if you need space for a changing bag or shopping. If the shops / baby clinic / playgroup are at the end of the street then fine, but any further, and I would suggest you buy yourself a more sturdy pushchair to walk with.