Quick questions on Financing

I'm new to the community and I have a couple of questions on financing. I'm relatively early in my self-funded search process and was wondering what the best timing is to engage with a banker about financing? Is it helpful at all to engage prior to identifying a target transaction?

Also, in comparing SBA vs. non-SBA lending, what is a typical down payment requirement for Non-SBA loans without a personal quarantee.

Thanks in advance.