Sequels generally don't tend to be long running nor longer than the original ones, thats a fact.
Second it also depends on the popularity finale of NNT might be the worst but it still sold around 300k-400k copies per volume so that's actually a good number(tho it's nothing compared to how much it did in its prime) and I'm damn sure the sequel manga won't be printing that big numbers, probably 100k+ per volume on average so such ranges won't axe the manga but it won't be long enough as well.
Third is the plot, which we don't really know about at this point but going off speculations it'll probably be having 2 major arcs which might be the holy grail arc and definitely the final arc and if nakaba brings liberty enough to bring some other wordly entities then it might have chances to go on, but again it will be dependent on its sales, rank and popularity, if nakaba brings any other worldly stuff then the rankings might go down, like I'm not saying as a guaranteed fact but just look at boruto it brought in other worldly stuff but is constantly falling (the anime revenue is the only thing that's keeping it alive)
Fouth if the manga comes out in a monthly or bi weekly issue then it'll generally tend to be much shorter and things would be wrapped up within 120-150 chapters
So my final conclusion is no matter how I look at it, I don't see it being any higher than 200 chapters long it would be shorter infact