Hi pomegranate1975 - I have worked with mostly 3-4 year olds for the last 15 years or so.
In terms of literacy development- for children between 30-50 months we would expect that children would start giving meaning to their marks (so not necessarily 'writing' but say you gave him a paintbrush, he might start making some brush strokes then point & saw "it's a cat" (even if it doesn't look anything like one!) They might start identifying their own name, and recognising some of the letters from their name when they see it in other places.
There is such a wide range in terms of development with these skills & your son sounds like he is right on track. Honestly I wouldn't worry too much about the academic stuff right now.
The best way to support him would be helping him develop his independence with self help skills, giving him opportunity to develop social skills & confidence (taking turns, making friends, joining play)
Providing as many opportunities as you can for him to problem solve independently: Think of a task that he might find tricky- putting his own shoes on is an example for some kids. Stay nearby & talk him through it, even when he struggles and gets frustrated, help him to break the task down into small achievable steps.
Help him develop critical thinking skills and the ability to make mistakes & know that these are an important part of learning. Let him know the most important thing is to always try & to keep trying- even when it is hard.
Give him the opportunity to be creative- make messes, experiment with textures, tools & techniques. Thinking about the process & what he is experiencing rather than what the end product looks like.
Make up silly verses to familiar songs that you know. Have fun with language, rhymes and jokes. Visit the library as often as you can- get excited about books & the wealth of information you can get from them.
If you focus on developing & supporting his learning dispositions (attitude to learning) then the academic stuff will come quickly & naturally, and if there is ever something that he ever finds difficult you will both be in a really strong place to fix it.