Actually I am changing up my force, that post is old. I do have a stormlord now. At the time, I reasoned that a tank regiment wouldn't be issued transports (because what would they use them for?) so I didn't have any.
FW has said that in the Solar Auxilia, however, some regimental commanders use Stormlords simply because they are roomy and faster than Leviathans, so that convinced me to get one as my regimental command tank, so now I have one.
I have some tanks with 2x sponsons, some not. If you are putting an Auxilia Tank Commander in it, bring both sponsons and put heavy flamers on at least the front two, because tanks that can overwatch with heavy flamers are awesome, plus whatever you've got in the boot.
If you just want a Stormlord by itself with Knight allies, that is possible with the Leviathan detachment; however, you get no Auxiliaries at all.
I would recommend, if you're using the regular Age of Darkness
FOC, a Lord Marshal. The ability to pick a warlord trait is very powerful, coupled with a Solar Auxilia Tank Commander means you can have a BS4 Stormlord which re-rolls 1s to hit (the trait you would get from rolling a '5' on the Command Traits table in the rulebook).