Hi,
Let me answer each question one by one 
1.) You can set this as a one-time purchase option and set the free shipping rule in your Shopify shipping rates.
2.) You can set this as a subscription with a discount (in the subscriptions app) and take the free shipping from your Shopify’s shipping rates OR set the free shipping in the delivery profiles configuration in Seal Subscriptions app. This allows you to override shipping rates for your subscription items.
- & 4.) These 3-Pack options can be set up as a separate variant on this product (e.g. 1-Pack variant and 3-Pack variant) OR you can set up a volume discount in Bundler app, so that you give customers a further discount when they buy 3x of 1-Pack item