Yes you DEF want it to be up to code and inspected. Don’t want to have to dig 450’ worth of trench twice.
When we buried our cable to the shop, it was laid out for 100amp single phase service(IIRC 4awg wire), sheathed, and encased in sch 20 PVC conduit some odd 4 ft down. Although I’m lucky if I draw more than 50 amps at a rip with everything running.
Also look into whether three phase is available at your line. If it is I suggest looking into having that run to the garage. Three phase, while running more voltage(typically 230-400v) runs less amperage and turns out to be cheaper. Running 3phz compressors and welders is nice :tongue We didn’t have 3phz service available here, too far from the main line grid.
From what I understand not a whole lot inspection is necessary other than an electrician to come up and check out the fuse panel and Nat Grid to be happy with trench.