I suggest competing a few times before playing with the bars and find out if you have any significant push (understeer) that needs to be addressed. Disconnecting the front bar may be all you need while retaining a stock rear bar.
As far as brakes I have never seen or heard of brakes fading at a rally cross event. Events are just too short to generate a heat problem. Braking on dirt is easier on the system than stopping on pavement as you don't need to apply the same amount of pressure as they will lock up sooner than latter. In my opinion, race fluids are complete overkill for rallycross. Yes, you should have fresh fluid (whether you're rallycrossing or not) in your brake system. Castrol LMA is a step up from stock replacement fluids and costs about the same (which is still quite a bit less than race fluids). I (and lots of other people) have used Castrol LMA in stage rally cars.