Thanks!

I filled both sides at the same time. The magnets at the corners helped as they were 4.25mm thick, as i could clearly see how much i should pour to achieve 5mm thickness.
As the channels that connect the sides were very thin and i have not mixed enough epoxy, had to mix second time and pour in the channels.

if i was to turn back time, i would have used the same aluminum angle profiles, fix them with scotch only from outside and use cheap epoxy with a brush to make a kind of base, which would close the distance from the channel to the profile against spill. When dry and so secured, pour over the expensive epoxy :-)

Yes, i welded the frame , the process is described at post #43. My second welding job in fact. Good that i was careful there, now things are much more easier that could have been with not so careful welding. used a cheap 250A Mig which i obtained from ebay+C02, hence the not so smooth welds.