Very nice progress! The decision to contribute to an HSA is rock-solid.
I have one question and one suggestion:
Question: What is making you lean towards the Roth over the traditional IRA? That post that you linked to from the Mad Fientist was actually what convinced me to switch from Roth to Traditional (both in my IRA and my 401k at work where they offer a Roth).
Suggestion: have you considered travel hacking with credit card miles and points?
Since your spending is so low, you might have a hard time hitting some of the spending limits, but there are ways around that (e.g. you can use the credit card to send money via paypal to someone you trust and then they pay you back, there is a fee to do this, but you can use it to meet the sign up bonus of the card and get $700+ dollars worth of free travel)
Some good resources:
