@Naydi, I'm so so sorry to hear about the crash. How incredibly frustrating! It's a real shame that auto-save... doesn't. As for the purpose of gardening, in addition to helping to raise Social by talking to the plants, you can also sell the harvests. It's not much money but in a challenge like this one, every little bit helps.
@Xx_LumiNati_xX I did something similar to keep Yuni svelte. Her diet consisted of mostly scrambled eggs and garden salads. She rarely ate until full (fully filled Hunger Bar) and almost never ate until her Activity Circle was complete (it was usually about 75% complete). I tried my best to stop her (occasionally, if I wasn't paying attention, she gobbled up the last bits). She was never allowed to eat anything even remotely fattening. She rarely exercised. I bought her a treadmill and punching bag, both of which she used, maybe, 4-5 times before I put them in the storage room (no room in the challenge house). Although I did not take pictures before or after, visually it does not appear that she gained any weight at all.
Good idea about the Energized showers and doing equipment-less exercises, though! Smart! Too bad our Sims can't Dance Off the Pounds or workout via a TV show.
@Zarriel, never too late to start. Good luck and have fun!