There are two safety standards for car seats at the moment, one is older and allows forward facing from 9kg, the newer one is often called i-size, the safety of them is a bit better and the minimum age for forward facing is 15 months.
You are best off rear facing as long as possible for safety. If you really really have to forward face, I'd stick to the 15 month guideline as an absolute minimum.
The Nomad is really intended for situations like taxis or countries where nobody uses car seats, where your other option is nothing at all. I wouldn't personally use it as a main car seat. It meets the older safety standard so it's legal to use it from 9kg even though it's forward facing. It might be suitable for you to use for lifts etc but it is quite minimal in safety. The problem is this in between stage is a bit of a pain because the seats are so huge and bulky. Would people pick you up from your house and be able to help you install the seat? Would you be able to install a standard belt fitted seat, like Graco Extend R129 for example, or Joie Stages? (You can see fitting videos for these on youtube). This would be safer as it has a rear facing option and meets the newer safety standard.
Are you looking for one seat to do both the isofix + rotate and being able to easily move to other cars? That's a bit difficult to do in one seat. The isofix, rotating ones are big, bulky and heavy. I think it would probably make the most sense to get an isofix, rotating one for your main car (most of these are the newer safety standard and they have both rear facing and forward facing capability) and then a cheaper, lighter one for using in other people's cars, perhaps the travel type one if you need it.
There are some which come as two parts - isofix base + the seat module which clicks in on top, like Joie i-Harbour. This can end up an expensive way to do things, though.
Another option which might work for you would be to look at impact shield type seats, like the Cybex Pallas seats. This is what I had when I was a non driver and I found them really good for swapping between cars, though honestly with my later DC I just got public transport everywhere. Most of these are suitable from 9kg, some are i-size so from 15m onwards, and supposedly they have lower force on the neck so possibly less risky for younger children, though this seems to be balanced with higher chance of the baby coming out of the seat in a crash and higher force on the abdomen area, so some people don't like them.
I do second checking if your LO has definitely outgrown your baby seat as they can last longer than most people assume. It's OK if their legs hang over the end as long as their head is contained in the shell of the seat.