I can't give an official response, but I can tell you what's likely:
1. You should have no concerns here. I can't promise Si won't release a second version, but I'd be very surprised if he did, seeing as he worked for so long on the current version. Si does release a lot of patches in comparison to any other game developer, but that's the great thing about NSG, as most developers would let bugs live for a few months and then deal with it. So yeah, don't let it deter you.
2. Online modes have been tried before with Sensational Soccer... I don't know about this one, I'm sure it'll happen in a future NSG title one day, but unless Si's got a sustainable model already planned for it, the cost of a server and other factors will probably stop it from happening for NSGP.
3. There's a track editor already in there.
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"The cardinal doctrine which they seek to teach is that souls do not die, but after death pass from one to another; and this belief, as the fear of death is thereby cast aside, they hold to be the greatest invective to valour."
- Julius Caesar