A literal follow-on to the Old Testament would assert what you have asserted.
The New Testament is much freer. It is voluntary, not legalistic, and as the Holy Spirit prompts. Money is a handy medium for giving back to the Lord, but there are other mediums such as service or miscellaneous chattels.
I look askance at legalism. It can result in giving too little a blessing rather than too much.
I agree with you there. I'm a fan of conservative theologians but they often have a legalistic tendency. Sometimes, there is a fine line between obedience and legalism.