You aren't going the most competitive way to start. The
MT starter box is better as
MT then as
AM.
can
That being said... Maybe you could look at building towards the Emperor's Blade Assault Company. That is 2nd tier competitive, and can make use of the Taurox.
So for a next step, I recommend this:
https://www.games-workshop.com/en-US/Astra-Militarum-Cadian-Armoured-Fist It gets you a Chimera and a Squad of vets, and runs about $55.