Best way to buy and sell using Kraken?

So I'm about a week into my crypto journey. Not super invested yet as I'm feeling my way around the market, the CEX, the different cold storages, etc, etc. Just learning as I go. I've learned that using Kraken Pro is the cheaper way to DCA in as you use lower fees than the instant buy I've been using. My question is do you need to do a bank deposit in order to use Kraken Pro? No debit card purchases like I've been doing? Assuming that's the case then how long do bank transfers typically take?

Follow up question. When I decide down the road I want to pull money out. What is the difference between the Kraken "Sell" option and the "Convert" option? If I "Sell" then I imagine it puts that amount in my Kraken account as USD, right? Doesn't convert do the same thing? Convert your BTC into USD? I guess the TLDR for this one is "What is the best way to convert BTC or ETH to USD within Kraken, when I decide I need to?"

Thank you folks. Been a fun week long journey so far. Lots to learn, and loving it so far!

FWIW: I'm going for a DCA strategy, putting in monthly, as opposed to day trading. Not sure if that matters. Maybe just straight debit card purchases are best for DCA?