Bit unclear about some of the information you have given but flux core tig wire is used for rooting butts that require a backpurge ie stainless steel without a back purge. The flux core wire creates a slag over the root bead to prevent oxidation or "cokeing" this wire is normally 2.2mm dia and if you look square on at it it looks like a bullseye. In the UK it is called super root, and in Australia TGX. The wire is really good if the welder operator is skilled in the technique and can be used to get repairs done and also if the butt is impossible to purge but mostly for repairs. I would ask for a 3.25mm gap use a used electrode to gauge, with a 1 mm land edge (if possible) you best have a good fitter on it if its a repair cause you know the score, you will get a 6 - 8 mm gap on site from some!
Now on your Amps it depends on your pipe thickness etc but for example here 2 " i would be sat on about 95 amps,all welders are different so up or down 10-15 depending on how you weld. you can do this free hand or walking but free hand is prob the best way, Have your set slopeing up 4 seconds and down 5 or 6 seconds,you can control your arc better whilst welding and you will not blow through,you need to strike up burn into the repaired edge or test coupon bottom tack and then wash up into the wall hold your tugsten there until it feels like you are blowing right into the butt at this point is where you will get your wire in there and dont be shy get a fair bit in,then move swiftly to the other wall wait for the same like your almost gonna blow through then wire.... repeat this all the way up wall....wire...wall...wire etc and you will have a nice bead even though it feels completley wrong,just remember once you have started dipping each side you will be moving pretty quick and the put in of the wire has to be perfect other wise you will get unfused flux. so move the wire as you move the tugsten so it is paralell with it ready to go in.
Hope this helps,been a while since i done it
Root only with this wire.