I have some ?s about OpenWrt wrt3200acm

"The 17.1.4 build not installing over the stock fermwair is not the falt of openwrt it is because the OEM changed the flash chips in the newer wrt3200ac routers after the 17.1.4 fermwair was put out."
Then maybe the OpenWRT people could have posted something about this on here https://openwrt.org/toh/hwdata/linksys/linksys_wrt3200acm
So then people looking to buy a router with the intention to install OpenWRT don't waste time.

As for OpnSense I have been hearing a lot about it over the later 2 years.
I've been meaning to ask my pfSense friends about it.
I have only worked with pfSense.
After looking at the pros & cons of pfSense vs. OpnSense
I have to say that's a hard one for me because I like some things about both of them.
So I will have to think long and hard about that which one I will pick.

You might also want to consider "bare" FreeBSD and ipfw and potentially netgraph.

Given that you're in the business of "penetration testing", a firewall that is doing its job properly should be blocking egress packets of the types at least I'd be trying to send. Can't test to see if a remote system if vulnerable to, for example, inappropriate IPv6 padding if you can't try to send that packet to the remote system.

I work from home & I need my router to be setup in ways as to not get in the way with what I'm doing at the time etc....
I also do projects & it's nice to have more control over my router then what I get from Linksys firmware or something like that.

I would not go "bare" FreeBSD for my router.
If I were to go down that path I would go with NetBSD.
My friend in high school made his router with an old sys running NetBSD & many of my friends in Europe do it this way as well.
I may do something like that someday but not now.