Easy to use yourself too HELOC works (there may be some places that do a HELOCs on rental properties)I personally have used a 401k Loan on a few occasions - You're essentially borrowing money from your 401k and paying yourself back (interest goes back into your 401k as opposed to a bank) and if you don't pay your 401k back the loan would simply become a withdraw (maybe some tax penalties, but you could probably finagle a workaround).

My main goal is to build good fundamental knowledge so any and all help is appreciated!

I'm a local real estate broker, investor, and manager (100+ rentals, mostly Airbnb/STR and multifamily).House hacking is a tried-and-true method and in Sacramento you can produce some meaningful income while enjoying the appreciation and tax benefits of owning real estate.

I am building a monthly passive cash flow for my retirement.   

For the residential side, check nearby apartment rents and recent sales of similar mixed-use buildings to get a sense of value.

I'm building some currently (so obviously I think that works). 

Too risky for us.Regarding additional guest packages, you can easily change your tax situation by offering what the IRS calls "significant services".

I work for a building materials company now and took their online game from Zero to very engaged in the past few years and it's been really fun.

You can play with it and build up a 3d walkthrough.

Picking up 3 properties. 1 remodel/rental, 1 demolition/New construction and 1 that I'm hoping to build a duplex on.