Yes, the waggoniers are planning something. They are by far the most effective military Russian group. So, having them sit in Belarus dosn't make sense. I believe that there is a chance that they could invade Poland. But if they do, the little waggoners will be going against NATO. That won't bode well for them.
They will more likely invade Ukraine again from Belarus. Putin won't dare take on a NATO country. That would be a recipe for losing Belarus, if not triggering a global nuclear war.
Putin's speeches about Poland not being a real country, owing their existence to Russia etc. etc. is very reminiscent of the bullshit history lessons he gave before invading Ukraine. So it is troublesome.
I see the two as grounded in Putin's ultranationalist perspective on history, where Catherine II essentially gobbled up much the Polish-Lithuanian Commonwealth at the end of the 18th century, a process that had been going on for a while. Much of Poland, like Ukraine, became part of Russia. It had a lot of Catholics, Jews, and other minorities that had to be dealt with, but it was officially Russian territory. Then Russia lost its empire after WWI and failed to get the Polish part back except as a vassal state after WWII. Poland, Belarus, and Ukraine were carved out of the Russian empire, and Trotsky's Red Army invasion failed to get Poland back after the Revolution. Belarus and Ukraine did emerge as independent states, but under Russian domination. Putin is the ultimate revanchist. In his dreams, he is the tsar who gets it all back for Russia. In reality, he thinks he can get at least some of the old empire back. That's one reason why Ukraine can't become a NATO member. He really sees at least eastern Ukraine as part of Russia--Novorossiya under Catherine II.
Could be a bluff to make Poland more wary of donating weapons to Ukraine in case they need the ammo themselves. Or it could be that Wagner will conduct false flag operations that make it look like Poland is attacking Belarus, thereby pulling Belarus to the war against Ukraine. Or whatever else. But regardless of Poland, having one of Russia's elite military groups on the northern border is still troublesome. They might try to attack south and cut off supplies coming from Poland to Ukraine. At least it forces Ukraine to keep some of their troops in the north-western corner of the country just in case.
I agree that saber-rattling at Poland is likely a bluff, and the attack to cut off supplies would be a reasonable strategic goal. Attacking Poland would be pointless, since it is a member of NATO, but the supply lines are fair game.