Buying domains and 301 them to target domain, how many?

So as the title says I am buying domains with good trust and incoming links in my niche and 301 them to my target domain in order to boost that website.
My questions is: How many domains can I redirect to my target domain before I might get a penalty? Am I safe if I do this for 10 domains? Or should I have maximum of 3 or less domains redirected to my targeted website?

Any input is appreciated.

I doubt you would get much benefit from three domains, and 301'ing multiple domains tends to be part of a churn and burn strategy.

True, will test out a few and see if there is any movement in serp.
Maybe put up a domain network with the domains instead?