I'm afraid this is a bit of an how long is a piece of string question. All babies are different and sleep for different lengths of time so there is no set amount of time they're supposed to sleep for.
There are loads of different theories about how much sleep babies need. New borns can sleep 20+ hours a day for the first few days or even weeks. This gradually gets less as they become more alert and aware of the world around them. DS1 settled to about 12 hours a day by 6 months while DS2 can sleep 18+ hours a day even now at 19 months.
With DS2 we took the approach of listening to him and settling him to sleep when he appeared tired (yawns, glazed eyes, grizly etc) and made a very clear distinction between day and night for him, with night feeds given in the dark with minimal talking and settling stright back to bed. We did this right from the start and he's been a fab sleeper and even at 19 months will still have 2 long sleeps in the day as well as sleeping through the night. He seemed to settle into a 3 hour routine during the day but some days it was less, some days a little more.
Best bit of advice I was ever given was to keep the bigger picture in mind over the first few weeks when their sleep patterns are all over the place. What you're aiming for is a baby that is happy and comfortable enough to settle themselves to sleep and will sleep through the night and have long restful naps in the day. Consistency (but not necessarily routine) is key imo. Self soothing to sleep and the difference between night and day are things that babies need to learn and not all get it at all - not a failing on mum/dads part, some babies are just poor sleepers (DS1 was and still is at 4.5 years).
Not sure about the sleeping on her side thing, maybe its frowned on cos she might roll onto her front. While she's tiny you could prop a rolled up towel of something to stop her doing that.
Hth and congrats on new bubs