This is just spitballing, you've already solved problem you set out to and get full marks.
There are always many different ways to do things with bash/shell. Here, you could probably do the entire thing in AWK, which you seem to already be aware of. This might be more readable or it might not.
If this were a script someone wrote for more general usage, I'd recommend to use the unofficial "bash strict mode"[0], and make sure to check that the awk/sed calls succeed. Shell has a nasty habit of limping along as far as it can if something goes wrong along the way and it's very easy to just end up with bad output and not notice until it's too late.
Another thing I only recently discovered is envsubst, a tool that's commonly available and tailor-made for substituting variables. You could pipe a template string or pile into that instead of the repetitive calls to echo. What you have here is fine and instantly readable, but if it were three times as long it might not be so nice. Here you could use awk to extract the variables and envsubst to put them into your template.
Honestly I don't think shell is a good language for writing perfect, robust things anyway. But it's good for exactly what you're doing, though, writing something for yourself that solves a problem without spending too much time on it (although it's fine to spend a lot of time on it if you're learning and/or just enjoying yourself).
[0] http://redsymbol.net/articles/unofficial-bash-strict-mode/