Where to buy?
I have a bank account and a debit card. It was easy to buy in Coinbase pro although I didn't like the long hold times.
Coinbase Pro also doesn't offer DOT or a few others I'm interested in and is a custodial wallet which I see it is not recommended.
What the best exchange where I can link my bank account, send money to it and buy Crypto in California? Or are there any places where I can do this with my debit card? Is there an easier/better way?
I am not certain about this because I am not a citizen of US, you can try bittrex or kraken, they are both US based exchanges too. They both support Polkadot as well.
https://coinmarketcap.com/exchanges/bittrex/https://coinmarketcap.com/exchanges/kraken/It's funny, many of the articles and videos I came across recommended wallets that are in your "not recommended list" like Exodus, Trust, Mycelium and CoinBase Pro.
Check the link below to know that this forum still comment good about mycelium. The link is mycelium wallet board.
https://bitcointalk.org/index.php?board=231.0Exodus and trust wallets are close source wallets, which means there source codes are not available to the public, which means you do not know the code the both wallets are using, if you trust them you can use them, but if there is a malicious vulnerabilities inputed by the developers, you will not know. But, open source codes are available to the public, they are the ones that should be trusted.
Coinbase pro is an exchange. But, if you mean coinbase.com custodial wallet, it is not also recommendable because not your key not your coin. You need to have full control over your coin, but such wallets will tell you that you have the full control but they can freeze your account because you do not ha e full control over custodial wallet, those that have the private key to the wallet have the full control which means only people that owns coinbase.com have the full control. There are possible ways they can even block your account. But, on noncustodial wallets, you have your private key and you have the full control.
I'll also get a cold wallet once I have enough for it to make sense.
It will be good, they are one of the safest wallets. Like Trezor and Ledger Nano, they support bitcoin and as many as possible altcoins.
So, I'd like to buy DOT (which is proving hard as it is not on Coinbase Pro) along with BTC and ETC mainly. Can I do this with a bank account, one exchange, and an Electrum wallet? Am I missing anything?
Electrum is not an exchange, it is a noncustodial wallet that is recommendable, you can not buy cryptocurrencies directly from bank using electrum wallet. Also know that electrum only support bitcoin. You can try Kraken or Bittrex like I mentioned above, then sending your funds to noncustodial wallet. If you have hardware wallet, then you can use it with electrum to support all the cryptocurrencies you mentioned.
But if I am eventually transferring to cold storage, does it matter too much?
Do you mean transaction fee, normal fee will be charged. What hardware wallet will encourage is the safety of your cryptocurrencies while online wallets are more vulnerable to online attacks.