Question
There will be 100 SKUs and 200 shipments daily via USPS First Class mail. All shipments are under 3 lbs; 80% of shipments are under 1 lb.
I'm curious about which software we should use to generate labels based on orders placed from a Shopify store and which software we should use to track inventory as orders are fulfilled, provide tracking information to customers, etc.
Answer
Try the guys at theprintful.com they have made a good niche business providing the services you seem to be needing. Best of luck, learn from them and keep asking questions ;)