You have good information here, and I would add as @Hels20 suggests, this is vital, and if you can dig in person, chatting to various neighbours as your own detective, you will discover more than the solicitor could be expected to know. The 'whose boundary' question is a potential future vexation, too. Also, local talk will know about the peculiar no-man's land of planning intentions which will go ahead, and will affect you, but which have not been formally processed by the local authority and therefore won't show on standard searches.
On a similar point, the standard enquiries before contract may be limited to immediate proximity, whereas the intention or even the fully approved plans to do something may be technically outwith the area covered, but would very much make a difference to your decision. e.g. a mega development which will bring construction traffic and noise for years, then swamp the quiet neighbourhood with a vast additional population, and devalue the peace premium you are buying.
With a newbuild, there are chances of faulty construction. Disgracefully, developers routinely demand purchasers sign non disclosure notices, as a condition of doing repairs, with the deliberate intention of not letting word get out about all the faults.
However, the idea of asking the seller is of limited value, since a) they may not be worth suing and pursuing and b) it may not be provable that they knew, even if the rest of the neighbourhood did, and c) in the case of neighbour disputes, as long as nothing is actually on record, they could later say they got on well with all neighbours, even despite any 'occasional misunderstandings'.