[X] Yes.
[X] An outside hire, specifically a mercenary captain.
[X] Trying to make the lordlings neutral again.
Nice update.
The premise of the first question is that some wars are justified and when given no choice (like during an invasion) one has to fight to defend his lands, his home and his family. Only the Arians (Polish Brothers, extremists that broke off from Calvinism) opposed all wars, even defensive ones, the rest was absolutely fine with defense. Fighting the French or Imperials as of now is a doomed venture. Lets stir the waters a bit and see what will happen, taking away the lordlings will leave them open to anyone for grabs later on.
We are a Radziwiłł. We do not need outside help. We have whole regiments, whole private armies merely waiting for our next command and one word would be enough for our dad to give us as many men as we need to lead our own force. We have German, Scottish, Swedish, French, Polish, Lithuanian, Spanish and whatnot officers by the dozens in our employ and finding one to be our second should be an easy task to accomplish. Indeed, there was a tradition, that many regiments were only nominally commanded by their high-born Colonels, when in reality those were purely ceremonial functions and the regiment was lead instead by a competent professional Lieutenant Colonel. While this became massive a bit later, it existed as well during these times.
Fun fact: The Dubinki line maintained a purely Scottish Guard Regiment in later years to protect their residence and Scots were abundant in their private lands. One of the biggest concentrations of Highlanders and Lowlanders in the whole Commonwealth served the Radziwiłłs and gave them plenty of recruits.
One more thing: when it comes to addressing us, there is the important matter of offices, that we will surely gain one day. A proper (and neutral) way of naming would be Prince [insert office]. So for example, Prince Cup-bearer, Prince Marshal, Prince Voivode, Prince Hetman, etc. You do not use this when addressing the man himself however, only when talking about him in third person (and without him present). For instance: I heard that the Prince Hetman (instead of Krzysztof) will lead a new expedition to Muscovy next year.