There are two (actually three) separate aspects here: the go-around actions (i.e. the actual aviating, flying the aeroplane bit), navigating a missed approach procedure, and finally diversion planning/execution, and I would suggest breaking them down as such.
Firstly, the go-around actions themselves: you are absolutely right to want to practice as the all-engines-operating go-around is probably one of the most commonly stuffed-up manoeuvres in aviation! At typical landing weights the average jet is very sprightly when full thrust is applied and things can happen very quickly. It is well worth rehearsing the go-around actions (by touch) as part of your approach preparation/briefing, before you start your descent: if you do so every time you fly you will soon have committed the actions to memory. You should ensure that you have set the initial missed approach altitude on the FCU once you are established on the approach (i.e. GS green on the FMA).
Assuming you are going around from relatively low height (as this is ironically the most straightforward scenario), the sequence is very simple:
On the decision to go around, the call is "Go around flaps"
Set the thrust levers to TOGA, verify that the thrust increases and you get SRS | GA TRK on the FMA and rotate towards 15 degrees (and follow the FD SRS commands).
Retract the flaps by one step
Once you have a positive rate of climb (and not before!) - gear up
Verify that the missed approach route is being tracked (i.e. select NAV or HDG as appropriate and verify on the FMA)
At the Missed Approach Acceleration Altitude, select climb thrust (LVR CLB will start flashing, just as on takeoff). The speed target will now change to Green Dot and you can clean the aircraft up as appropriate.
Verify that the missed approach altitude is captured (ALT*/ALT annunciates on the FMA).
The aircraft will automatically re-string the approach in the FMGC for another go if so desired.
As for tracking the missed approach route: this really is just the same as tracking any other procedure. Like anything else you do you should brief/plan the missed approach procedure as part of your approach briefing so that you know what to expect and can anticipate any potential traps (e.g. a very low missed approach altitude, complex tracking requirements etc). The missed approach procedure should be automatically selected and available when you select the approach in the FMGC and nine times out of ten you can simply track it in NAV mode (obviously ensure that the database matches the chart and that what the aircraft actually does matches with that!). Note that often ATC may give you a heading or other instructions if the traffic situation means that the standard missed approach procedure on the chart would bring you in to conflict with another aircraft, so be prepared to follow such instructions if necessary.
Finally, when it comes to diversions -- again this is a question of prior planning; again as part of your approach briefing you should have an idea of where you might go if for some reason you are unable to get in to your intended destination and how much fuel you will require to get there, and don't forget you can also enter the alternate route in to the FMGC. If there is ATC available they may just give you vectors or a direct to a convenient point. As far as the aircraft is concerned, simply do a LAT REV and enter your new destination. After that, it just becomes a case of planning and executing an approach at the new destination, so it will be very busy but otherwise exactly the same as planning an approach anywhere else! The main thing to bear in mind is your fuel situation as you will likely be running close to final reserves at this point.
As for your question about planning for a practice detail -- all you need to do is load sufficient fuel for whatever it is you are planning to do. There is certainly no need to do anything with PFPX etc -- indeed if you are planning to fly a number of go-arounds/circuits then PFPX is not really set up for this at all as it is designed to give you a plan for a point-to-point flight.