Yeah I saw it... he looks cute. That's great he's eating well. You can make fruit and veggie puree too (don't use the premade stuff from supermarkets, its very bad for them) make you own at home using a blender, that way he can get used to the taste of fruits as well. Mango works well for this

The feathers under the beak and neck will come. Eggfood actually makes them stick together so you need to make sure you mist him regularly and give him a shallow dish of water to bathe in within his cage, it might be just that their tangled up. If the feathers are getting matted get some warm water, perhaps some aloe vera if you have a plant (don't use synthetic aloe vera and NEVER soap) and paper towel and gradually tease out the dried egg food. This happened to our cockatiel George, he was fully weaned but couldn't understand how to drink so we had to give him the eggfood for a while.
As for pooping; observe the movements he makes before pooping. When you get a stand you can put him there as soon as he does the poop dance! You can click when he does this on the poop spot or give a treat.
Or you can just stick to putting the towel underneath him, however be careful as this may lead to him holding his poop in so personally I prefer just to watch for the poop dance and catch it but many people do it successfully. There are many threads on the forum about this so take a browse of those.
The advantage is their poops don't smell (unless there's something wrong with them) so it's not the end of the world if they have an accident. If he does poop somewhere undesired you can just place him back on the stand. Punishing the pooping can lead to them holding their poop in too so it's a delicate process. Again read the topics on how this is done correctly.
Your paper technique will help.
Great news you're getting him to an avian vet too! Well done!