I'm a quite paranoid guy to say the least, so my idea may sound far-fetched but if I had that much money, I would definitely spend as much time as I could securing my funds the following way:
First of all, I'd take some programming courses. The main purpose is being able to audit
by myself the code of a given software.
Next, I'd choose Electrum as the software to go after and audit it entirely. This is in my opinion a very important step, especially when you have that much money to hold. Another option is to audit
Ian Coleman's tool, but I'd still go for Electrum.
I'd then create a few airgapped, strongly encrypted PCs to store my coins on. Wi-Fi and any other wireless module removed. Metal case, as tight fit and enclosed as possible to block most frequencies/signal to and from the external world. Probably somewhere between 3-5 PCs in total, each having a different encryption password and wallet. I'd also get some resistent metal sheets to write the seeds on them, and webcams with lids to scan QR codes rather than manually inputting an address/tx data or using USBs.
And finally, a PC with Whonix (or Tails) on it to sign transactions through Tor. And that's basically it. If you've audited the code of a software by yourself finding nothing suspicious and also created some secure PCs that cannot communicate with the outside world, the risks are significantly decreased.
For a hot wallet, I'd choose Trezor. And once again, auditing the code is helpful. It feels great as it's offline and the risks are smaller with it than holding your coins in an online PC (this excludes human errors, obviously, such as accepting a tx without checking the address characters multiple times or the amount you're about to send), but I would personally not trust it for that much money. A PC that
never connects to the outside world or external devices (besides keyboard/mouse/webcam) is imo way safer.
My answer for the idea of holding a lot of money on custodial wallets is a straight, bold
no without a doubt.
