You'll probably be surprised to hear how important benchmarking / diagnostics are for motivation. Not just at the beginning but along the way.
One of the biggest problem when you take a new, unfamiliar challenge like the GMAT is a lack of sense of progress on a daily basis/ weekly basis. This is where coaching / classes can really help -- even if it's just for guided self study (not full blow tutoring).
If your prep is centred around real-time diagnostics then you'll feel measurable progress even when you can't yet take practice tests or even complete complete practice sets.
Reach if you want more personal guidance. Happy to have a no-strings attached personalised conversation with you.