Spend only a few hundred dollars on stamps, envelopes and notepads and handwrite the letters yourself. 

That being said, if you could obtain a general prequalification letter from a lender I would hope that would suffice.

You will have to let any existing leases  expire before you can raise the rent, or send them a letter a week or two before it expires inviting them to sign a new lease at the new rate.

Hi,So I recently completed my first wholesale deal and am starting my first yellow letter campaign.

Get an authorization letter from the owner, call the servicing company, and find out exactly why the short sale was denied.

If you insist on using LLC, there are some banks that can give you a rate and LTV with similar or better terms to what you mention with 20-25 year amortization that balloon in 10 years.  

Pay stubs or employment letter.

Send them a hand written letter.

From the requests I've been BCC'd on, it's not like you need a preapproval letter to see a disclosure package. 

1) I would guess commercial, however your bank would tell you if they would let you "slide", getting the 4 plex in your name would open you up to getting a 30 year loan rather then the business 5 or 10 year balloon loans.2) To change retail to residential, you need to talk to your local zoning officer, and probably building inspector.