For bathing, getting the cheapest shower stall is fine. I started wooden shack one that uses solar power one, and I tried the most expensive bath and shower handmade one, etc. I ended up with Vampires Shower because it seems to increase my Sim's hygiene meter the fastest and it is the prettiest.
You can only take tepid showers regardless and it almost always gives my Sim a red uncomfortable moodlet.
Taking a shower at the waterfall makes the Sim feel grimy and uncomfortable too.
I always deal with it by doing something that overwrites the mood a lot.
The best way to shower is by Scuba Diving or Free Diving. It is extremely cleansing and increases the Fun Meter super fast.
You can also simply swim but it is slower at increasing the hygiene meter.
Basically, I only use the shower stall on my lot once every 2-3 Sim days because there is far greater benefit to go Scuba Diving for seashells.
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I do my best make my Sim wake up with all needs fully green, and I spend the entire day on Scuba Diving or swimming around to take photos with the $2000 camera.
The profits from selling seashells and treasures from yard sale table is around $3000 from 12 hours of seashells/treasures. I have found that setting 200% profits on seashells gives a steady flow of customers. 300% mark up is a hard deal to drive and you end up feeling very tired with the sales pitch. If you set to less than 200% markup, the customers will take the items on their own so that it is easier that way.
The Salvadorian table is $100 cheaper than the City Living table, and looks better with Island Living.
And the profits from photography from swimming around all the islands until my Energy go bust is an average of $20 per photo. If you click close to 100 photos, you can increase photography skill from Level 5 to 10 in one shot. That means about $2000 (to "buy back" your camera) and about 2-stars in Get Famous.
If you go photography after that, everything is profit. This means that you can lead a relaxed island life to do what you want but ALWAYS remember to take 5-10 photos a day to get a couple of hundreds to continue living.
You can really live the way you like - lazing around, do nothing. But if you want to get rich and famous, and build a millionaire's house, shift lots, etc, you have to continue the daily grind of 50 - 100 photos a day.