There are pros and cons of using both methods. Both methods can produce potential "problem areas".
Seeing as you probably don’t have a press break.
I would just weld the two parts. What I always do when you need the welds to be strong is to grind the edge of the plate. Seeing as its 5 mm plate you would be fine with welding it in one run instead of a root run then a weave over the top.
So it looks a little something like this.
Slightly exaggerated, but a quick rundown the one edge of the plate, but you will be fine without doing that, but it only takes 30 seconds.