I store things like scores and lives as individual base 10 digits myself. Addition and subtraction are easy (simpler than converting binary to decimal, IMO). It may seem like a waste of precious RAM at first, but realistically speaking, how many displayable numbers do you need? Most games only have a handful of values to display in the status bar.
If you're really hung up on converting binary to decimal though, this has been discussed countless times in the forums, so try searching for these discussions (
the most recent one is just a few days old).
As for displaying text, there's really no secret behind it: each symbol you can display is a tile (you can only display symbols you've included in your CHR data, along with the other background elements of your game), so in order to display a letter you just need to write the index of its tile to VRAM, using PPU registers $2006/$2007, like you would for any other background element.