Since prices are down, I am going to spend some money for shopping. Not a lot, just what I can spend.
Now the question is, should I buy BTC (currently I don't have any BTC) or should I do DCA for ETH, SOL or DOT?
Since you already hold some other coins but no bitcoins yet, I would strongly recommend to buy some BTC. Right now the BTC price is cheap compared to last year. If you can buy BTC below 30,000 USD it's a good deal on my opinion. And BTC as the oldest crypto coin should be part of any crypto portfolio. I am assuming you are looking to build up a long term portfolio and not only want short term gains. For that BTC should definitely be part of your wallet. We don't know which Alt coin will be successful long term, but we know that bitcoins will still be around in the future, it's never a bad investment.
Not only bitcoin should be part of every portfolio it should also be its main investment, after all even with the bear market the bitcoin dominance is above 44% and if we did not considered all the shitcoins, centralized coins and POS coins then that dominance will be even higher, so with this in mind then it is important to take bitcoin seriously and make it an important part of your portfolio otherwise your long term results will be disappointing at best.