No need for workbooks, or writing. The great thing about them being interested this early is that you can do what they're interested in and leave other things for later. Mine had periods when she was making strides with number, and other periods when she was more interested in reading. I feel sorry for EYFS teachers who have to show they're making progress in every area of the curriculum at once.
Mine knew alphabet and some digraphs similarly early (the first time she actually articulated a c sound was to tell me there was a c on a sign). She wasn't very interested in doing anything at word level while she was 2, but announced at just turned 3 that she wanted to read.
We were lucky in being very near the library, so we went in every day and worked our way through the "early readers" section. I don't know if your library is doing the same as ours during lockdown - we can order books on "click or collect" - you can either give specific requests, or ask them to select, so you could ask for a pile of "early readers". Libraries are the best thing for early readers - you want to be reading lots of different books, so there's not much point in buying them - the stories are not really worth re-reading.
The Apple Tree Farm books went down very well, though, especially at the beginner stage: she used to read "what people say", which tended to be the easier words and was a good way to share the reading. That works quite well on harder books, too, so you're doing most of the reading but he tries little bits. (It also means you can read more interesting stories than the ones written for learning to read.)
Numbers beyond 20 - I think our main thing on that was that I got her to find the hymns in church! Snakes and ladders would be good - probably other games too. Also, look at house numbers when you're out for walks.
Mine still couldn't hold a pencil properly when she started school, and could only write letters that were made of straight lines. She could use a computer to type and spell words, though, and was quite happy about upper/lower case. She started school writing her name in capitals, not because I'd EVER done that, but because she couldn't manage the curves of the lower case letters, so she chose to use the capitals instead. As she learned how to write them in her first term, she swapped them - you could date her artwork that term by how many lower case letters there were in her name!