Jingle Bells, my door-to-doorbells saleswoman went around making sure that everyone had upgraded doorbells, silent running dishwashers (not too many of those) and fireproof stoves and fireplaces, as these are the fastest upgrades available in Sunset Valley.
Her traits were:
handy (obviously)
loves the outdoors (mood bonus)
loner: (mood bonus)
slob: (no need for showers)
computer nerd: (faster computer upgrade)
She joined the firefighter career, and then promptly took 5 days off. She took a class in handiness, and then tinkered to level 3, adding a couple of bonus upgrades to her score. She stayed in the career until Sunday afternoon (day 1 week 2) and then quit, having done the extinguisher and alarm upgrades, and also getting her weekly pay.
I think I might have missed some possible upgrades, or there's a trick I missed, because some people had more unique upgrades than I thought was possible with the restrictions - for example the brain enhancing machine is banned, so no upgrades possible there. And the PlasmaPunch Gyroscopic Conductor can only have one upgrade on it, instead of the two different ones. I didn't quite reach the LTHP for even the food replicator, so I decided to skip that and the teleportation pad, and go for pure upgrade count. I skipped one or two others, because they took too long I think. Basically if I could get more single doorbells in that time than a single unique upgrade could offer, then I skipped it. The scoring adjustment meant I got more unique ones though.
One important thing to know was which items have a 15 minute upgrade time. I read about it in one of the old challenges - the ranch toilet that came with pets is one of them. The bath/shower that comes with seasons, or the shower that comes with Mastersuite. There are a couple of fireplaces that do, too. Also, the kareoke machine only takes 15 minutes for singing synth, but the sim keeps upgrading. You can cancel after 15 minutes when one of the bars is full.
For time management, my sim napped in the rocking chair for fastest energy recovery, and ate lettuces when hungry. I left some of my unique upgrades to do during the wee hours of the morning when I had been kicked out of someone's house after 3am.