PlayStation 4 - Parental settings

I'm going to answer some of your questions in a different order than they were presented and also wanted to link you to this overview on PSN Family Management:
https://www.playstation.com/en-us/network/family/

When I create the child accounts they lose all the saved games and downloaded games that are under the main account.  

This is not entirely accurate.

Downloaded games are accessible to all of the family members. For example, I have a  Family manager (parent) account on PSN with around 100 games downloaded/installed. My daughter's child account has access to all 100 of those games.

Saved game progress is associated with each account, correct. So if your kid plays to "level 10" in some game under your parent account, then saves that game progress, they can't switch over to their child account and load the "level 10" saved game progress from your parent account. Or if you buy some custom "skin" for a character inside of a game on your account, you can't share that skin with all of the child accounts.

Is there anyway to set restrictions on my main family manager account?

I don't believe so. Everything I've seen shows that "adult" accounts can't be restricted. Even other adult accounts under a Family Account aren't able to be restricted.

In these screen shots you can see what kind of "parental controls" are available on my "Family Manager" account, compared to my daughter's "child account":

Family Manager (Parent Account) Settings:

Child Account Settings:

If I had to take a guess at a makeshift workaround (which I can't guarantee would work) -- you'd need to somehow trick Playstation into thinking your family manager account was a child account. There's probably a setting somewhere that controls your birthday and you'd have to set it to be under the age of 18. Then you'd have to invite that child account into a different Family Account.

I don't know that is even possible though, as I doubt you can change an adult account into a child account.