Right after I closed, I transfer it from my personal name to my 100% own LLC.Recently, someone mentioned doing that will subject to some kind of transfer tax or stamp tax?

I am sure others will have some good tips but I would recommend outlining ahead of time what your walk through process will be with the tenants.

If you're presenting an offer and the other party accepts, you have a binding contract that is subject only to the contingencies you list. 

That is another subject I have read a lot about and follow what Warren Buffet has done, and trying to adopt similar strategies for my own investing.

If you are 1031 exchanging, you can do it at any time, subject to the identification rules of 1031.

@Judy Parker there is an attorney in Morris County that specializes in NJ tax lien issues, Micheal Pellegrino is his name, he wrote a book on this subject as well (NJ specific).

A lien under this subchapter does not attach to:(1) wearing apparel;(2) tools, apparatus, and books of a trade or profession;(3) schoolbooks;(4) a family library;(5) family portraits and pictures;(6) one couch, two living room chairs, and a dining table and chairs;(7) beds and bedding;(8) kitchen furniture and utensils;(9) food and foodstuffs;(10) medicine and medical supplies;(11) one automobile and one truck;(12) agricultural implements;(13) children's toys not commonly used by adults;(14) goods that the landlord or the landlord's agent knows are owned by a person other than the tenant or an occupant of the residence; and(15) goods that the landlord or the landlord's agent knows are subject to a recorded chattel mortgage or financing agreement.

I would like to make the jump from my single family rentals to development of small multifamily, but information on the subject is hard to come by. 

Clearly seen by the example I've just outlined we allow for a significant amount of upside/equity for our clients. 

The best book I can possibly recommend on the subject is Ken McElroy's ABCs of Real Estate Investing.