Just on the snagging - we had a new build by Persimmon once, a good builder. We snagged the house ourselves, we did the entire process three times. PIL helped, went over house with absolute scrutiny and there were over 200 faults the first time, the second and third times we found some we missed the first time and had to go back again and again and again and again to get some things fixed.
Note, if you are near the end of the development it is VITAL you get the snags fixed before the builders leave the site, otherwise you won't get much progress. You need to be back and forth to the property manager, don't just trust for ANYTHING to happen. They will say things will be done, they won't. It is a nightmare. Our builders mostly knew us by name we were there so much to be done.
You can bargain with snags, to get extra stuff done. My next door neighbour actually had an entire window missing because the builders accidentally forgot it! Some of our faults were very small but important - a barely visible hairline fracture in a white bathroom floor tile. The company tried to say it didnt matter, but we argued we paid for a perfect tile not a broken one and over time that fracture would shift and get dirty. It matters. We agreed not to have the entire floor redone, and instead they upgraded some other stuff for free.
My BIL has bought 2 new builds, he became very hard-headed about it. He said, don't be embarrassed or shy about negotiating. They expect it.
Remember some snags re major and cannot be fixed and are an opportunity to negotiate by threatening not to complete. One of these is the plot itself, often I've heard of gardens having gardens cut off vs plans etc. With his second house, my BIL's snagging list included "garden is shorter by 140cm than the plan measurements we were given.' Builder mismeasured at the front and built the house too far back , which meant a very short garden. You can't fix that, so instead they renegotiated the price (buying less land, less saleable in future). It was a major hassle. But you literally have to snag EVERYTHING.
You will learn absolutely loads. Definitely pay for a professional snagger if you are not experienced. Also, remember the property company simply wants to make money, so anything they can get away with they will. They RELY on you giving up so they will string you along, promise and not deliver, tell you it is fixed when it isn't, try to persuade you the fix isnt important, try to say, "well you didnt pay for that" , try to tell you that it is "a normal part of the building process" . You are both up against deadlines so use it to your advantage, don't take no for an answer, stay on top of the snagging list remediation with in-person visits as much as you can (phone and email ok sometimes, but the more you can physically turn up on site to pester the property agent the better, as they won't want you there complaining while they are making other sales).