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.
The Bitcoin fees doesn't really matter if you plan how you DCA properly.
However, i don't advice unnecessarily leaving of fund after buying on centralized exchange. What you should is to not withdraw your Bitcoin after every DCA if you want to cover less fee on your every purchase. Instead, you can do the withdrawal to your wallet biweekly, monthly or every 3 months.
A few weeks or month won't be that risk, but you also need to be vigilant as centralized exchange are being attacked these days.
Its rare to see this concern since actually fees doesn't really matter if we invest on Bitcoin for long term because we are not affected with this matter.
I guess the people will get affected with these are the traders its because they are the one deal with Bitcoin for short term and might their trades might get affected especially that they cannot execute their trades because traders might get worried to pay huge fees for their trades and other short term transactions.
This is the advantage of long term holder since we don't have any major concerns towards issues which currently occur on the market.