How much overlap is ok to hold 2 ETFs?

I have some questions, but the biggest one is the title.

1. I have SPY and SCHD, and recently found out around 50% of holdings in SCHD is also included in SPY. I understand the weights are different, but still, they do overlap. How much overlap is considered ok?

2. I'm 27/M, and probably will be working into my 60s. At the moment my retirement plan is to live off dividends from my assets. I know in the long term putting everything in SPY and selling it all to buy dividend stuff gives me a better chance of higher total return, but I feel too bothered to plan all that. Will putting some of my money in dividends from now affect the total return after 30~40 years that much?

3. Currently, I own stock based ETFs, bitcoin and bonds. I am thinking about starting to put some money in REITs in around 5~10 years. Other than these, are there any other form of assets that I should consider holding?

Thank you to everyone who put time to read/answer this!