#Strike is one of the most cost efficient for stacking that amount at least in the USA, but I don't know about their fees or deposit options in other countries.

I withdraw to Phoenix wallet over lightning. The request incoming liquidity feature in Phoenix will save you money on miner fees.

I let it pile up in Phoenix until I can move at least 2 million sats to cold storage at once in order to keep those UTXOs large. That will matter a lot in the future.

10 years from now it will be very unfortunate to have a bunch of 100k sat UTXOs in your cold storage. Keep them at least 1 million sats.