Fixing rusty door shut.

[superloopy]

Well now ... i've had a v6 for a couple of years now, unloved in every sense by me almost from day one. It's now showing the dreaded rust around the inside panel of the osr door quite badly. Nothing visible from the outside yet but when you open the door .... aaarrrggghhh! So ... i've decided to have a go and at least cut it out and if it needs to go the garage afterwards then so be it. Question is ... i need an angle grinder, yes? What's a good small, slim tool to do the job? As for a patch ... I've got an old rear door panel in the same colour. Could i use a piece of this and how to shape it? I know a couple of you out there have already needed to do this. This is the third car i have to show the same problem. It'll not get through another mot in this state. There is a thread on here somewhere where the patch panel was pop riveted in place but i cant seem to find it? I'm guessing that a weld is the way to go but if i can at least try and prep it ....