I don't see anything wrong with politely asking someone if he would be interested in joining an exp party.
At certain levels on RDM and PLD, it was a common occurrence to receive invites out of the blue. At most, I was slightly vexed when the /tell consist exactly two characters: "PT". It annoys me somewhat that people can't even be bothered to type a question mark. Otherwise, if I have something else to do (which I usually do), I politely decline.
I'd advice starting any inquiry with an auto-translated
◀Excuse me...
▶
Of course, BRDs are different--they are so popular, they all have paranoia about unsolicited invites.
So, leave them alone, but can ask other jobs.
* * *
As for knowing where to go, that's great, but it doesn't hurt to solicit party members' inputs, either. "Want to camp at ____? What do you guys think?"
Most of the time, there should be no objections, but every once in a while someone will point out something which may be over looked, like five parties of same levels in zone, someone may be too high/low for the camp, DD's are piercing damage and should fight flying critters, etc.
Building consensus on where to go and how to fight before heading out is how Japanese players like it, so just asking the question may help put JP members of the party at ease as well.