Bitcoin Core supports creating a custom signet and mining utility for setting up a public test network with alternative functionality. This is not meant to be used to create an altcoin with actual or perceived monetary value as I (and many others) would recommend using a sidechain rather than attempting to start a new currency.
Right now, I manage to run ...
I advise you just to rely on https://github.com/dgarage/NBXplorer/
This is an API more flexible and more stable than Bitcoin Core to manage HD wallets. There is a C# client, and it integrate nicely with NBitcoin.
You can create PSBTs from it, ready to sign with NBitcoin. (Disclaimer: I am the main maintainer for both NBitcoin and NBXplorer)
You set the fee rate to 6 sat/vbyte. That's very low, median fee in recent blocks has been 30-70 sat/vbyte. See mempool.space.
You could wait until the weekend when the mining difficulty is expected to drop by more than 25%. This will decrease fees as more blocks can be mined per hour. The difficulty drop happens around 1AM UTC on Saturday.
One of the problems of Java is the verbosity of the language. However, it is also true that the life of the language it is very old in these that.
I fall into the problem to talk with the bitcoin rpc interface for one of my side projects on c-lightning and I was not able to find a clean library that is able to talk also with other rpc interfaces derived from ...