HB Smith or Weil McLain are very good gas-fired boilers. If it's a cast iron boiler, than it's probably made at the same foundry so that's not gonna be an issue.
Just shut the switch down at the boiler in the warm months unless you want to pay for gas. (There may be a pilot light, unless it's electrically started.) There's no preventative 'thing/things' you need to do when you do this.
As for verifying my findings and professional background, not. Run your question by a few folks in the boiler-installation business. I'm basing this info on living in New England. And it's good you have separate units for heat and hot water.