What would be a "good" minimum amount to avoid blockchain spam ? I will read about Lightning Network and see if I can use it. 
If this is still correct, the minimum amount to send it 546 satoshi (0.00000546 BTC / $0.04). If that's your 2% fee, that puts the minimum payment amount at 27,300 satoshi (0.00027300 BTC / $1.98). Unless you don't charge a fee for lower transactions, or set a minimum fee.If you receive such a small transactions in fee by yourself, you'll have to consolidate them at low transaction fee, otherwise you risk paying more in transaction fee than it's worth.
To compare services, you can check out Paywall.Link. They accept micropayments through Bitcoin Lightning Network. Their Recent list shows what you're up against: most of it looks like spam.
