Assuming that the order was intentional (attack first, then declare war), why did Japan decide to do things that way? Obviously it gives your side a one-time advantage, but wouldn't it also reduce your international support due to breaking "the rules"? Is there any record of deliberation on the Japanese side where they weighed the positives and negatives of that approach?
Japan knew that speed not strength of arms would win against Russia. Even though Russia outnumbered the Japanese in almost everything it was all in the European side of Russia. Taking Port Arthur would give a strong defensive position and another port, it would also give Japan something to bargain with and show off its spoils. Knocking out the only army in the area and minuscule fleet would make sure they controlled the area.
I haven’t read anything that made an international outcry to Japan’s movement to Port Arthur before the declaration of wars. The pre-emptive strikes would not be seen as “illegal” till Hague 1907. The meeting was postponed because of the Russo-Japanese war. But I do know that Russia almost caused an diplomatic incident with the UK when it’s Baltic fleet attacked the British fleet, mistakenly thinking it was Japanese.
While the world was shocked that Japan attacked Russia, it was more shocked that an Asian power attacked an European power like Russia. It’s shocked them even more when the Japanese beat the Russians