There's a shop in NJ that does undercarriage restorations all day long on Toyotas. Coatings and welding if necessary. After doing some of that myself, I think I'll gladly pay for someone to deal with the rust dust and paint fumes.
That being said I think the best course of action if you decide to DIY is an angle grinder with knotted wire wheel. Grind the crap off and then treat with Ospho. Then Rustoleum Rusty metal primer, and then satin black. Then protect that with PB Blaster Surface Shield. Getting a headache just remembering that process though.