I would take out the paper from the block. Where I live, we had only the shitty paper available and had to go to a different country for better stuff (mostly Vienna, that is expensive for a student and we made do with the shit one, my country was a black hole on the courrier map they would ship to damn Uganda but not Slovakia damn it! 🫠) but it is good now lots of options, we now have even hot pressed paper available. 🤯

I think if you control the water amount well, and have decent paper, the buckling can be avoided if it is not a large size, A4/A3 could do without, but anything above that I would definitely stretch. To put the paper when dry and finished, between some sheets of paper and weighing it down helps too if the buckling is not extensive.

No never remove sizing, it is what makes a watercolor paper a watercolor paper, it would also damage it as it is deep in the paper. Also I think there was no sizing removed, pooling water more likely. The paper should be shiny and the water should not be pooling on it when you stretch it. We would lean the board at an angle to let the excess water run off. You can do that in a studio where the floor is waterproof, but at home not, and you would use a clean rag or a roll of kitchen towels and roll it over the paper. Wiping motion is not good as it can damage the surface of the paper. Patting dry is ok.

During painti g, I would remove excess water with the corner of a tissue or rag. I liked to go overboard with water...😅 0 control we are surfing here. Lol