Most power companies will also provide you with a usage history for your account. This can be used to determine what your actual maximum load has been historically. It won't be anywhere near 200 amps.
Don't just add up the breakers. That's meaningless. Add up the appliances. Each appliance should list it's current or wattage requirements. If it gives watts, just divide by volts to get amps. A 60 watt, 120v lightbulb draws 60/120=0.5 amps.
Anyhoo, total your loads. The biggest loads are HVAC, water heater, washer/dryer, electric oven/range.
Even if you total more than 200 amps, you'll notice that most of these appliances aren't run at the same time.
At the same time, 100 amps is alot of service for a shop. Whatcha gonna run out there? I'd think 50 or 60 amps would suffice.