The chances of you quitting your 9-5 and doing real estate full time and being successful is similar to the photo below where everyone at the top in the crowd is thinking they can do it, and there is one person for every few thousand that can do it. 

thereby allowing these plumbing updates to pay for themselves).I've got the toilets and faucets all picked out (because I have personal experience with these and I know which ones are good) - but I'm not sure what to do about the shower heads...I know that shower heads are an item that can be the biggest money-saver (because these tend to consume more water than anything else).

You're income certainly isn't "normal" and some banks might shy away but this is a personal business and if you have a track record, I think you can find a bank to say yes.

Can I give a tenant written 30 day notice on June 1 (in person or taped to the door) for move-out on June 30? 

I used my personal cash for both , but I’m looking to purchase more with lending.

Lot of good house in east side of the bay is setup for a good house hack and it is still way affordable for Bay Area standard lol

@David Braut12% interest + 2 points and fees to draft documents is around industry standard.

I personally own properties in the counties of Orange, Los Angeles, Riverside and Kern.

LLCs offer no tax benefits, they mitigate liability and the fact that this is on your personal property and you'd be renting to yourself, there's no liability to mitigate.

If you could go in person that helps.