I have a similar project in mind myself in 1/72, avoiding 28mm (I've not enough space, plus I'd lose the chance to use a lot of model railway buildings etc.).
For small towns you'll likely want a number of simple, grey rendered terraced houses/shops with the odd Georgian/Victorian building for town hall etc.
I'd look at card buildings myself - possibly scratch-building - for the lower status buildings and bought-in one for the municipal buildings.
"Old Barracks" and Garda stations simple card buildings (again, a lot seem to be just rendered - so paint & a bit of fine sand mixed ).
For the old style, often isolated white-washed stone country cottages personally I'd scratch-build (inscribed cheap builders' foam over card, coat of PVA & paint. Teddy bear fur for thatch, model railway slates or corrugated card for corrugated iron roofs).
Landlords' houses & prosperous farms; Napoleonic/Georgian.
And lots of stone walls - and fuscia hedges..