If the leaves are healthy, the stems are healthy. They do turn woody with age - they never stay green for long. I don't think you've got a problem at all. Basil can take a lot of water - the important thing is drainage.

It looks like it has downy mildew. It also seems stunted for a squash. I wouldn't count on a crop from it.

You might have a fusarium wilt or other type of fungal wilt. I'm no expert but that kinda sounds like the symptoms. I think a kinda test for fusarium is to cut the stem open and see if it's all brown and dried up inside, like hollow with no middle. Google fusarium to see if this maybe matches what your seeing. It's possible your just overwatering and rotting the roots though you have to make that call. If it is fusarium treat it seriously and dig up the plants and throw them away. Sterilize tools etc with rubbing alcohol or vodka. Fusarium gets into the soil and overwinters, it attacks a variety of plants including mints and tomatoes too.

Hi Keiko, yeah, too little water or too much water, it leads to the same thing - the death of the root system, and the plant shriveling in that way, from the bottom up. Obviously Doug has the right advice and your plan is sound. You don't have to section the plant up into several cuttings unless you want to for insurance. I went through this with an elliptica this weekend and I just cut vine from the bottom until I got to a healthy section, where the vine wasn't shriveled and it bled well, and stuck it into my rooting medium up to the lowest node. I can't tell from your pictures if you actually have mealies. When you touched the white spots was it sticky fluffy stuff or was it dry and chalky? It just looks like dried sap to me. Yes, there are soil mealy bugs and foliar mealy bugs, but they are two different creatures from different families. (Technically, there are many different soil mealies and many different foliar mealies.) My point, though, is that if you see mealy bugs hanging out on your vines and leaves, these same bugs won't also be in the soil. Of course, you could have two infestations going on at the same time, but that would just be bad luck! The fungus gnats won't hurt your Hoya. Technically they do eat plant roots (as well as algae and fungus in the potting media), but they die off when you let the medium dry out, so they aren't a serious concern for Hoya people like us. But they are a sign that this pot has been too damp for too long. So, that's not good. You don't necessarily need to repot the healthy Hoya, since it's survived the ordeal, but you should let it dry out well and be watchful of how that decorative pot affects its water retention. Could be you just had a wonky period with your watering, or it could be the wrong setup. You just have to keep an eye on the situation and if that plant is routinely drying out slower than all the ones next to it, change the medium or the cache pot.