Good Morning
I certainly can understand wanting to avoid a daily commute from Concord to the Longwood area of Boston--moving to (or near) a border town will likely shave 35-45 minutes off his daily commute. Since you mentioned that you're fairly new to NH, I would just ask a couple of questions before jumping in with any recommendations.
Would taking public transportation be feasible for him? If so, the Boston Express stops at Exits 2 (Salem), 4 & 5 (Londonderry), with terminals at Exit 2 & 5. Getting from South Station to the Longwood area might be tricky, but could work... There is also a Boston Express that runs from Exit 8 in Nashua to South Station (just to consider towns on the west side of the Merrimack) that also drops at South Station & Logan.
Questions about things other than on your list:
What is your tolerance for things like going to the dump (transfer station) with your trash. You can hire a private hauler if the town you choose doesn't have public trash pick-up, but honestly, most folks I know love their weekly dump runs. They run into people from across town that they might not have seen in awhile, and if the town allows it, you can put your 'still good, but unwanted' items in a special area, where others will find a new treasure to bring home. I've been lusting after a gorgeous scrolled iron gate that my friend snagged at the dump last spring. And a garden club member got her hands on dozens of old bricks that someone was getting rid of. They were transferred from the back of one pickup truck into another, and now those bricks have new life as a garden walkway. Reduce, reuse, recycle! Yeah, trash pick up is convenient, but picking is a highly respected New England tradition
Another consideration is are you OK with private water & private sewer, or do you prefer to have these as public utilities? If you are buying, realize that you really should have a sewer inspection and water testing completed. While water testing labs have to meet state guidelines, septic inspections can range from someone digging up 3 shovelfuls of rock and deeming the leachfield to be 'pass' or 'fail', I would much recommend a much more comprehensive test that includes a push camera throughout each pvc line, and exposing the distribution box. It's a little more money, but considering that a new septic system can run 10k or more, I think it's money well spent.
If you prefer, or even require public water & public sewer, that will seriously limit the towns that you can consider. And while Salem has quite a lot of access to public water/sewer, many homes (even in your 400k price range) do not. Londonderry also has a few neighborhoods with public/public-very limited.
Schools, Rte 93 access:
Not knowing how old your children are, you might consider a town that contracts with Pinkerton Acadamy. Currently, these towns are Auburn, Chester, Derry, Hampstead & (most recently, Hooksett). Of these, my suggestion would be Hampstead, since he could easily access Exit 3 via Rte 111. Hooksett would gain nothing for you in terms of the commute, so should be dismissed. Auburn & Chester are nice towns with a rural feel, but are furthest from the highway.
I would definitely consider Windham (but realize that prices will be higher than neighborhing towns, and taxes are $$$ thanks in part to the new HS, built in the last 5 or so years, one of the top rated in the state). Perhaps consider Pelham and Londonderry too. Salem (like Derry) has a high percentage of rental units and trailer park homes. This is not meant to be disparaging, but studies suggest that some these parents may not be as vocal and committed to the educational process (which would include being knowledgeable on LOCAL budget issues, and attending town meetings and/or voting on town & school budget).
LOCAL CONTROL is a very important part of New Hampshire culture. It's not something that I've experienced anywhere else that I have lived. But I digress...
If you might consider moving west of the Merrimack River, I would consider both Amherst and Hollis. Hollis and Brookline share the middle school and high school, and is consistently a top rated system. Brookline is more rural, further from the highway and has higher taxes than Hollis, while Hollis values/home prices will be higher. Merrimack isn't as highly rated as either Hollis or Amherst, BUT I know many people who live there and LOVE their neighborhoods, their schools, and the town spirit. It's not the most convenient town for accessing the highway, due to the darn tolls that STILL exist if you're heading south on the Everett Turnpike.
Hope this is helpful for you