Yes, thats a pretty good sequence. If I were being even more paranoid I'd say the TailsOS should never be connected to the Internet, so put Bitcoin-QT on a USB stick before you start, and install it from that. Check the MD5 of the Bitcoin-QT on your USB matches a trusted source and you should be good.
Reasoning: if you're compromised while on the Internet downloading Bitcoin-QT, anything you do afterwards is unsafe, unless you're physically disconnected from the Internet afterwards. You say "disconnect from Internet" but if that's just disabling the Interface in the UI, thats not good enough and a trojan could easily re-enable it.
I physically unplugged my router and there isn't any connections that I can connect to around here but yes that does sound more safer!