My DS is in reception so can relate to where you are at the moment. At this stage of the year, our reception teacher is working hard to make sure kids are building up to meeting expectations by year end. Yours should be too. We're on school holidays still, and extra resources have been given to children who need help with a particular area eg sounds/numbers etc.
From what you've said, book band 3 (yellow) is the required expected level for reception year end. Sounds like he may meet this criteria or be very close.
Re: numbers, the expectation for EYFS is to count to 20, add 1, take away 1 etc. You could purchase a Numicon set to help him with this at home. My teacher provided me with a sheet of activities to do with him at home. Happy to share if you DM me.
I'd speak to the teacher and ask what s/he is specifically doing to help your child meet the expected standard, and also what you could be doing at home, if you want to that is.
In our case, my sons writing is pretty poor, made worse by him being left handed. We sometimes doing additional handwriting sheets at home (bought a book off Amazon), but I'm being relaxed about it at this stage.