Removing front seat concern?

Yes, and then to wait at least 90 seconds before starting any work, among other precautions against personal injury and property damage. I highly recommend reviewing at least these topics in the Repair Manual, available by subscription to techinfo.toyota.com:

• General: Introduction: Repair Instruction: Precaution

• Vehicle Interior: Supplemental Restraint Systems: Airbag System: Precaution
• Vehicle Interior: Supplemental Restraint Systems: Airbag System: DTC Check/Clear

• Vehicle Interior: Seat: Front Seat Assembly (for Power Seat): Components
• Vehicle Interior: Seat: Front Seat Assembly (for Power Seat): Removal
• Vehicle Interior: Seat: Front Seat Assembly (for Power Seat): Installation

• Vehicle Interior: Seat: Front Power Seat Control System: Operation Check

There are warnings about SRS (airbag) and other hazards, plus instructions on how to disconnect and connect the airbag connector, which uses a connector position assurance (CPA) locking mechanism.

Yes. The Location & Routing section of the Electrical Wiring Diagram (also on techinfo.toyota.com) shows the connectors involved, including Nb1 (Front Seat Wire LH), NZ1 (Front Seat Airbag Assembly), N87 (Front Seat Cushion Heater Assembly LH), and N90 (Front Seat Inner Belt Assembly LH). You can cross-reference these to the System Circuit section to see what circuits would be affected.

If you power on the car with the seat circuits disconnected, the power seat and seat heater systems won’t store diagnostic trouble codes (DTCs), but you can expect SRS DTCs B1656/38 (Seat Belt Buckle Switch LH Circuit Malfunction), B1826/56 (Open in Side Squib LH Circuit), and perhaps others.

 

Yes. Besides the system initialization from disconnecting the battery, you should check that the power seat works, check for and clear SRS DTCs, and if the passenger seat was removed, do the zero point calibration for the occupant classification system. That last operation requires a Toyota Techstream diagnostic system.

In general, I’d advise against omitting any step in the Repair Manual procedures unless you know why the authors might have included it and are certain that it doesn’t apply in your situation.

 

You’re right to consider this. Some shops may follow the automakers’ procedures to the letter, but I suspect many don’t, sometimes with unfortunate consequences for the safety and reliability of their customers’ vehicles. Would you want to sit in a seat with bolts that weren’t tightened to specification, or rely on an airbag with a connector that wasn’t locked in place and might come undone at the worst possible time?

Do-it-yourself work can be challenging and rewarding, but it’s good to think about your capabilities, in terms of skill, resources, and available time. Do you have the patience to plan, organize, and follow a hundred steps or more? If something were to go wrong—a broken bolt, stripped thread, damaged connector, or severed wire—would you be able to solve the problem? Would having the car out of service for a few extra days (or longer, if a part has to come from Japan) cause problems in your life? Would you be able to shrug off the cost of repairs?

Just as important are the effects of modifications, even if done properly, on the safety, reliability, operation, and resale value of the car. As I mentioned in a previous thread, the Prius and Prius Prime electrical system supports many essential functions, and I’d hesitate to add much additional load. It’s hard to say how much is too much, though, without Toyota’s proprietary design information, far beyond what’s available in the service manuals.

Indeed, while I’m happy to discuss modifications, for these and other reasons, I can’t recommend modifying your car at all, except perhaps by installing Genuine Toyota Accessories.