The mobile was branded to T-mobile but has been debranded (although i do get the T-mobile logo showing up on start up and shut down) but works fine with my local SIM card (Malta). The problems I have came up with are that when i try to use certain apps the googlemail of the previous owner still shows up, thus impeding me from using these apps...
1) Should i restore factory settings to get rid of this or will my phone become branded once again?
The easy answer is you need to get rid of everything on the phone, so a Factory Reset will wipe it clean and you can then setup your own Google account. If the phone was branded, then yes a reset will put the phone back in to its original state when new so it would be branded again.
(I understand that by doing this all apps will be deleted but i could transfer them to my PC before doing so with USB cable and then transfer them back?!?!)
No, apps need to be installed, not just copied back and forth. A Factory Reset will delete all apps, messages, history, call logs, etc.
2) Is there a way of knowing if there is a Goldcard installed on the sim?
There is a way to check, but since you're new it's probably too involved to check. I doubt it's a goldcard. But you can create a goldcard easily with a goldcard creation tool and then you have no doubts. You can then also run the RUU update file at the top of this thread and completely debrand the phone and install Froyo v2.2 which works great.
3) Is there a way of finding out what flashed version i have?
Sure, just go in to Settings, About phone, and post the "Software information" page so we can see what version you have and advise you of the best way to update.
I would also like to upgrade to Froyo and when i settings-about phone-system software updates-check now there is an update available Android 2.2 and HTC Sense update 89.36MB
4) Will this update bypass all the processess needed on the first page of this thread?
It would update your phone to Froyo v2.2 but it might be a branded version back to T-Mobile.
5) Will i need the Goldcard for this update?
Branded updates do NOT need a goldcard. But you do need a goldcard to unbrand and install a generic version of Froyo 2.2.