Ok well first off if you have ever overwatered and the leaves turned yellow cause of this the leaves will never turn back green. I would just remove the yellow leaves. If your getting wilt during the day that could be a sign of not enough moisture in the soil or to much sun. Young plants that arent well established sometimes do this even with the proper moisture. To much acid in the soil can cause a plants leaves to turn yellow. If this is the case taking some epsom salt and put it around the base of the plant will help that part. No the epsom salt will not hurt the plant if thats not the case. As far as your raised bed 2 gallons of water can be enough or not enough. It really depends, for one any kind of plant in soil that has completely dried out may take more water than that. When a plant completely dries out the best way to water is by a slow long drip. If you just dumped the 2 gallons of water on the area it may just not of had time to soak in. If an area is wet or has been watered consistently and the ground is not completely dried out it will take less water to reach to the bottom. I really hope that made sense. As far as a soil moisture meter I personally have never used one, I tend to listen to my plants. If they want water they tell me if they wont less they tell me. I dont get to technical when gardening trial and error is my way to go. I try something if it doesnt work I try something else.

We don't mean to overwhelm you w/all this info. But there are certain basics required & proper mix (soil) is key. Sadly the mix you're thinking of using is awful for succulents. As you've been told sand is awful for them, so is 'regular' potting soil. Also particle size matters, it's best when materials are close to the same size, helps uniform drainage. What's shown in your link w/ pix of large & fine mixed together will impair drainage. The fine material will clog the air space in the mix & prevent the roots from getting oxygen, which the plant also needs along w/ light & water. Yes, many here will suggest 50/50 cactus & succulent mix combined in equal parts w/ perlite. This will give good drainage. So will 'gritty mix', as it's called here, which has several recipes to make your own which you can search for here. Pls. read up on succulents & learn that they have the ability to store water in their fat, fleshy leaves, so they don't need as much watering as many folks think. So when it comes to when to water, in succulents we say, when in doubt about watering, don't. Wait several more days then water. Using a sprayer (if you mean a mister) isn't good for succulents, best not to wet the leaves (encourages rot). Also best to water into the soil AROUND the plant, not on it. Sorry for all the details, but mix & drainage are super important in growing succulents; & usually the first correction folks need when they start coming here.

Like Rina mentioned, it's natural for the bottom leaves to wrinkle up and dry. Your main concern should be giving these guys more light, and higher ventilation. Singapore has a really hot and humid climate. Does your pots have drainage in them? Are you pots made of clay? Clay Terracotta allows the soil to dry faster.

I will likely repeat some of what was already said, but here are my comments: 1. container needs to have drainage hole 2. layer of pebbles at the bottom doesn't help (if, only temporary and not enough). Best to be avoided. 3. good idea mixing purchased soil with perlite (or pumice, or gravel or few other, inorganic ingredients) - looking at the photo, it looks too 'fine' = often water retaining. Pls. note that I am only judging what I see in photo, and not being able to see it directly. 4. it is usually best to get rid of all old soil from the rootball. even washing it if difficult to remove. Spraying with garden hose helps :) Any damaged rots should be cut off. After, let roots dry up on something absorbent, in shade rather than sun. Good air circulation will speed it up. Few hrs to overnight is usually enough. 5. It could have been potted in smaller pot, but it should be ok since pot is not too deep. Big pot = lots of soil, and it may take longer time to dry up. 6. Do not put new succulents into full sun - unless you know for sure hey have been in sunny position before. Always acclimatize them. 7. Water when potting mix is almost completely dry: get a bamboo skewer/chopstick or even pencil. Insert deep into pot (at least 3/4 deep). Leave for few min; if clean and dry when pulled out -time to water. Watering depends on the temps - mix will dry up faster in hot weather; amount of potting mix and even pot - glazed pots take longer. 8. Some reddish color on leaves comes with good sun, and is desired by many of us. Just remember to acclimatize it in order not to burn it. Jades are very easy plants to grow. As with all succulents, give them great drainage and light and they will be happy. Do not expect overnight change - it will take a bit for plant to recuperate from repotting and it also depends on your growing conditions. And above all - enjoy it, do not worry about 'testing' it every day. Any further questions, just ask...:) PS: you will likely get best suggestions on Cacti and Succulents forum - growing other plants in garden is quite different than growing succulents in the containers...