Or maybe that would be a nice tradeoff between starting at SF10 and then allowing TTN to send an early LinkADRReq by only using a confirmed uplink soon after the 20th message.
On the other hand: after your first tests with ABP you’ll probably want to switch to OTAA. For OTAA, you could start at SF7, after which LMIC will try a worse SF if SF7 fails. More on that in ADR and gateway distance that I linked to above too.