Hi @haejin, where are you storing your USD dry powder and where do you buy your BTC when you're ready to deploy? Do you have a method for buying other coins directly with USD, or do you have to buy them with BTC? How long does it take to deploy once you start the process?
The only method that seems to be available to me is buying BTC/ETH/LTC through Coinbase with USD, and each purchase takes about a week to process.
Exchanges like Bittrex, Bitfinex, Coinbase, etc.
Coinbase is one of the few well known places to buy that keeps an actual US Dollars (USD) Wallet. They charge you out the ass to buy directly through them, but sometimes you gotta do what you gotta do. If you use your Bank Card instead of your Bank Account to buy, it is instant. They do have a much lower limit of how much you can deposit with each card per week, but it is instantaneous. Most exchanges don't keep a USD Wallet...this keeps a separation between the USD and the exchange, and keeps from possibly infringing on US laws. Instead, most markets have USDTether (USDT) Wallets. This currency is supposed to be backed by real US dollars, and keeps within a couple cents of $1.00 USD at all times. I believe Kraken lets you buy and keep USD, but I don't use Kraken, so I'm not 100% sure on that. Here is an article explaining USDT: https://www.cryptocompare.com/coins/guides/what-is-usdt-and-how-to-use-it/