You only need to understand that centralized exchanges or centralized peer to peer marketplaces have their minimum trade sizes, that you must know and afford to meet it. Later you will have to meet its minimum withdrawal size so that you have clear ideas on how many times of DCA with a same small capital size for being allowed to withdraw your bitcoin.
It's also cost of withdrawal fee to make sure your withdrawal value is big enough to cover withdrawal fee to make the withdrawal fee on your withdrawal is not too expensive. If you make a withdrawal and withdrawal fee costs 50% or 70% of withdrawal value, it's too unwisely.
Exchange withdrawal fee shouldn't be a barrier to any investor no matter the little amount ($10) that you have to invest into bitcoin, because you have to leave your funds in the exchange for it to pile up to $500 and above before sending it into your self custody wallet to avoid many small small UTXO that will later turn around and bite you on the ass in future when transaction will be very high. You might end up using all your profits to pay for transaction fee due to poor transaction management.
I could remember two years back when Rune and BRC-20 token congested bitcoin blockchain, the transaction fee was fucking high. That shouldn't deprive you from your regular DCA weekly purchase because definitely, transaction fees will go back to normal and you can transfer your bitcoin to your private wallet.