i am not expecting any SSD to be worn out unless the previous owner was into heavy workloads, which isn’t the case for a lot of mac users. You can technically write over the whole SSD hundreds of thousands of time before losing some capacity. Assuming the OS runs on BTRS you’ll be fine as the file system will auto flag bad sectors.
The battery is definitely replaceable but in latest models used to be glued on… I haven’t checked on the Apple silicon models… worse case the Apple Store can do it for you for 70/80€$ You can also remove the glue yourself, there must be an iFixit tutorial on YouTube for it