I am not sure about Avocado - I don't think it is toxic but isn't a good thing to feed - there are better things.
I am not sure he needs extra protein to be honest. Older hamsters don't need as much protein and too much protein can lead to kidney problems. If he is eating a good hamster mix with the correct levels of protein then he won't need protein supplementing.
Fresh food supplements are always good but I would stick to veg, pumpkin seeds. Soft food could be baby food or a bit of porridge. A bit of scrambled egg weekly won't do any harm. Baby foods need to have no onion, garlic, spices, tomato or citrus/lemon juice. The age 4 monhts ones are mostly ok. The cow and gate sunday lunch and chicken and pumpkin ones are fine
Also the hipp sweet squash and chicken.
Just whatever he fancies really but not lots of high protein foods - kidney failure could increase fluid and strain on the heart.
As they get older they may not be eating much of the dried hamster food and mainly pouching it. But keep putting it out and it can be a good idea to also get some Science selective - put a few pellets in a baby food lid and add a drop of water to soften them before putting it out - they eat the softened pellets and get all the nutrients and protein they need from that - so then the baby food and other extras are just extras for enjoyment.