Capt. Hunt

nope, you don't actually need a tank on that stage, as long as the fuel can flow to the engine it will fire.  If I had to guess, I'd say that the fuel crossfeed is turned off somewhere, probably one of the docking ports.  If you have KIS/KAS you can bypass the crossfeed by installing a fuel line on EVA.
 
You may run into other issues with those docking ports though.  From here it looks like everything is connected with Clamp-o-tron juniors.  That thing is going to shimmy like a belly dancer when under thrust for more then a few seconds, because of how flexible the .625m joints are.  I'd recommend a minimum of standard clamp-o-trons to connect modules on large interplanetary ships.

procedural fairings has a script that automatically removes the 2.5 and 3.75 meter fairings and changes the 1.25 meter one to work like their fairings (does not seem to effect the 5 meter MH fairing base).  I know it's rather annoying, since there's some times where the stock fairings are still useful, and it breaks any rocket that uses stock fairings.  To get the stock fairings back, delete PF_Squad_Config.cfg.

I think the Kerbnet feature in stock does this.  Or, if you've already been there, you can plant a flag

I checked, just turn off the radio button that says "Enable Extra Groundstations" under the Advanced difficulty settings.