Quantifying the long term costs associated with self hosting the Bitcoin node?
Is there a practical way of quantifying the cost associated with self hosting the Bitcoin node? This includes the cost of hosting, scaling and hiring a competent developer to setup and debug the node.

Depends on the business. If it's a startup you can always hire a developer for initial setup. If you experience any issues in future, pay another developer per hour for a specific work.

What is a practical way of quantifying the long term costs involved and what type of maintenance/upgrades would a developer be required to do in the long term?

Type of upgrades/maintenance can involve anything mentioned on https://bitcoin.stackexchange.com or https://github.com/bitcoin/bitcoin/issues