Can't use Tails, other security OK?

Unfortunately I'm unable to run Tails. I use a chromebook, and it doesn't allow me to boot from a usb drive. I am running Ubuntu, however. Will I be secure enough if I browse with Tor in Ubuntu, use PGP, and send my bitcoins coinbase > tumbler > DNM? Is there anything else I'm missing?

I saw this post that asked a similar question, and the answers suggest that I'd be fine, but I wanted to make sure.

EDIT: Just to be clear, I'm only interested in making small, personal purchases.

(as a side question, should I be posting this through Tor as well, or is it enough to use Chrome's incognito mode? I'm not sure how paranoid to be.)

EDIT 2: Can I send my bitcoins directly from coinbase to a tumbler, and then directly from there to the DNM? Or do I need to use a blockchain wallet or electrum somewhere in there as well?