Building Lender Relationships

I have seen a lot of posts highlighting the lender process when using a SBA loan broker, but I do not intend to use one, at least to start, so am curious on the process for those who did not use a broker. I am kicking off a self-funded search and want to know how others approached lenders? Did you engage with lenders before identifying a potential business or submitting an LOI? Do lenders provide any sort of preliminary commitment letter (subject to further diligence, of course) to give a seller confidence I can raise the necessary capital? I intend to reach out to local banks and credit unions in my area, but also would like to hear if anybody has any recommendations for more national players (e.g., Live Oak, etc.)