Dust control off of a machine like your surface grinder would require a capture vent with a high transport velocity, like what you would see in a wood shop. Unless you are grinding chromium steel or special alloys, the health risk won't justify the cost.
An a/c system with good drainage from the cold side will dry the air in your shop, and heating in the winter will prevent condensation on your machines that lead to rust.
Your main health concern will be with the welding setup. TIG and thermal cutting processes put a lot more chromium-VI into your breathing zone than similar MIG processes, and TIG produces a lot more UV that can ionize various residues on your work pieces/surfaces as a secondary effect. Welding fume extraction systems are affordable enough for the home shop, and can also be fabricated by a HVAC contractor. The idea is to position a flexible 5-6" duct with a flanged end about 4-10" off of your work while welding using clamps or a magnetic base to hold the vent in pace, and exhaust the air outside. Look for 100 linear feet per minute at 6" from the duct face for fume extraction. You can accomplish that on 1/2 hp or less.
Canopy hoods in welding booths are not effective, since the fumes move past your breathing zone from the point of generation to the exhaust vent face. They will contribute to the total air change rate in your shop, but so will general ventilation.
You probably won't need an intake system for your shop (push-pull). There are enough leaks in most buildings to provide makeup air, but you are best off to add a square foot or two worth of passive vents down low in order to keep the power bill down. It won't take much to ventilate a 380 s.f. space. 30-50 CFM worth of throughput from an exhaust fan would do nicely, any more would pull the hat off of your head.