Just find the school that offers ED-Visa and is approved by Ministry of Education. The school staff will have do everything the agent would have done, for free
I’ve done 3 border runs this year, when you use an agency they have a success guarantee, the agency have a deal with immigration. But if you go yourself you might get denied after a few times.
I think that is wise of you, myself I can’t wait to turn 50 in 2.5 years so I can get the retirement visa. It’s a walk in the park compared to marriage visa.