If this is correctly set up, is the hardware wallet inherently more secure?
No, electrum cold wallet is also very secure and safe, if done correctly, both are safe and secure. Also, electrum in that form is a cold wallet while the other electrum is a watch-only wallet. You need to be careful of your computer not to have malware that can attack your hardware wallet during bluetooth connection for transaction signing. While I still believe more in electrum cold wallet signing with QR code generating from the watch-only which is malware resistant. Although, we still need to totally do all necessities to avoid malware.
Hardware failure?
All you need to protect is your BIP39 seed phrase, ones you have it properly backup against damages and attackers, and safe from loss. You can import the seed phrase on another hardware wallet or BIP39 supported wallet which will generate back private keys, addresses, bitcoin and other fund balance immediately.
Malicious attacks?
About malacious attacks, there are some vulnerabilities reported in some reputed hardware wallets, while also they can be attacked if your wallet extension device (the computer you use to access it) is having malware. An example is the malware that changes recipient's address to hackers address, that is why you need to check and recheck the address you inputed before sending. The malware can be trasmited through the USB while QR code is still resistant to such which is safest for transaction signing.
While the hardware vendor client database can be hacked, allowing criminals to come knocking on my door, can the same happen with Electrum?
There are some ways to buy hardware wallet avoid your information being given. You can read the link below for that.
[GUIDE] How to buy a Hardware Wallet the right wayAbout electrum wallet cold storage, electrum wallet can not be connected to your email, home addresses and the likes, I will prefer to make use of electrum cold wallet. But read the guy above for how to buy hardware wallet appropriately to be able to buy hardware wallet without it linking to your information.
Also, looking longer term, what would be the consequences of developers ceasing to maintain Electrum?
I do not think electrum wallet will cease to exist because it is well supported and developed by Bitcoin developers. But if there is any doubt, know that electrum wallet is an open source wallet, it has a
tool you can also use to generate the master private keys and private keys which you can be imported on other reputed Bitcoin wallet.
Should I also export my private keys, in addition to the seed phrase (with appropriate safety and storage precautions)?
You do not need to, ones you know the seed phrase that can be used to generate the private keys using some tools if need be. Like the link I posted above for electrum and iamcoleman for BIP39 seed phrases.
What other criteria should I consider?
Protect your seed phrase, do not let it lost, do like three backup that will make you to be able to access it anytime you want and also do all that are compulsory to make it impossible for attackers to steal.