You can't really rely on them. My previous school swore up and down they canceled everything after I left. Turned out, they canceled jack shit. It ended up costing me over 20,000 baht on visa runs and new paperwork before I got my new docs months later.
If you don't care to ever come back and work here again; no problem but I can testify from personal experience that it's a major pain in the ass if you want to return to work and don't cancel properly.
I see. I'd shop around for ins then. There have been a few posts about different companies and what they offer. Btw, most companies don't cover motorbike accidents unless you pay a really high premium.
If it's a WP, you'll be at the Ministry of Labour office, not immi. There has been no interview that I have ever experienced. You just submit paperwork and if everything is kosher, you get your WP.
You need a visa invitation letter prior to arrival. It can be obtained online but shop around. I had been getting the letter for $25 but my friend in VN got it for me for only $8. I'd been getting ripped off all this time and didn't know it.