] Mr.Bennet may've been intially abit harsh on Mr Collins. My impression was after reading his cousin's letter he didn't expect any sense from his guest.

In fact, Mr. Bennet says as much. When Lizzy asks him whether the writer of the letter can be sensible, he answers "No, my dear; I think not. I have great hopes of finding him quite the reverse. ...I am impatient to see him."

So he not only expects that Mr. Collins won't be sensible, he is looking forward to that. It is Mr. Collins entertainment value as an object of derision that he is anticipating, it seems.

] When they sit down to dinner with their guest, JA tells us Mr Bennet scarcely spoke at all. Perhaps Mr B. was weighing up Mr Collins' conversation?

After Mr. Collins' comments about complimenting, Mr. Bennet says, "You judge very properly, and it is happy for you that you possess the talent of flattering with delicacy. May I ask whether these pleasing attentions proceed from the impulse of the moment, or are the result of previous study?"

Obviously he is not openly rude here, but he is clearly making fun of Mr. Collins, although Mr. Collins doesn't recognize it. (On the other hand, considering the provocation, one might conclude that he was remarkably restrained. ;-))

] Then decided he hadn't the charecter to match his stated good intentions.

Sorry what do you mean by this?

] Ethics also decree the hostess should make her guest welcome as well.

Yes, but is it allowable to make fun of the guest?

] The entailment may've overshadowed some people at that dinner creating difficulties.