By teaching myself piano from scratch using John Thompson's easiest piano course, how many books do I need to get through to be grade 1 standard? I am currently half way through book 2. Thank you.
In this link, from the ABRSM forums, the first individual to answer suggests that it's the end of Book 2 and the beginning of Book 3 that is the ABRSM Grade 1 Standard.
You may also be interested in this thread from Piano World. Typically it's looked down upon to offer an outside link without a summary, but it's a little tough to summarize that thread; it goes off the rails pretty quickly and never really answers the original question sufficiently. But you might find some important information in there nonetheless, especially regarding some alternate method books that you might choose to look into.
In terms of pieces, you can try to learn some Grade 1 pieces first, and if those are really too difficult, you can do your Prep Test first. It's designed for beginners who have been playing for six to nine months, so you shouldn't be too far off from where you are. The preparation for the Prep Test should get you to the level where you can at least try Grade 1.
In addition to the pieces, you can practise sight-reading. You can sight-read almost anything if you do it at the right speed, but at your level it might be best to try to find beginner sight reading books, such as 'Join the Dots' for Grade 1 or the other ABRSM books available (I'm not going to suggest any others because I don't of any helpful ones in particular).
Scales are something you should be doing regularly, and you can always try the Grade 1 scales.