Attempting to get prequal/preapproved - anything to look out for?

[Akash Sky]

I've decided to take the plunge and invest in real estate, and want to do so by house hacking with a duplex.

I want to purchase sometime between summer and winter of this year (I hear that the holidays are the best time to purchase), and plan going to get a few mortgage preapproval / loan amount quotes.

I've got a few questions that I would love to have some light shed on:

1) What are some things that I can ask / look for in order to determine some intangible things about the lending institution such as:

a) Willingness to work with me in order to get my loan approved (i.e. if I'm not going to get accepted for a loan, I'd like the person to at least think if there is a way for me to get accepted)

b) Closing speed (i.e. how fast can the lending institution close a deal?)

2) Things to look out for / question in terms of closing cost (i.e. is that $10,400 real estate transfer tax legit?)

Also, if you've got any comments related to prequalification and preapproval, I would love to read them!