Seam welding is only required within 300mm of a 'structural area'.In order for a repair to be acceptable for an MOT test it has to be attached as per the manufacture. That means that a repair must be seam welded all the way around.
On a Minor that is the majority of places where they commonly rot anyway!
However it does allow for stitch welding patches on door bottoms etc... if/when desired.
As for learning - the front inner wings are as good a place as any! The rear inner winbgs are probably not a good place to start.
A lap-joint (overlap) will be far more prone to rot as the moisture trap will cause catalytic corrosion (due to the different % of dissolved oxygen between the edge and middle of the seam - if you're in to chemistry).
Therefore if you do lap joints (most people do!) then use a seam sealer and plenty of paint to keep the joint dry. Places like box sections often don't allow for sealing the joint on the inside so bear that in mind.
As for MOT passes - I've seen many repairs that pass an MOT but give nothing to restoring the damaged structure of the car. The MOT is based on what can be seen but it's far more important to restore what is structural.
