1. There's no "conversion" from LN to onchain. Is just a swap of sats, from a LN channel to a Btc address onchain. Sats in LN are the same as onchain. There' s no magic token or other thing. Just simply the same sats.
2. The swap cost depend of the mempool fees in the swap moment. That means you don't know exactly which swap service will be cheapest, we don't exactly what type of fees they use.
3. Here you have explained step by step how to make swaps https://darthcoin.substack.com/p/lightning-network-submarine-swaps

https://fixedfloat.com/?ref=wnp33zrc

Тебе это поможет!

конвертация BTC в Молния

Run your own node and Loop it out when incoming sats start filling it up.