Re: OpenWrt or DD-WRT?
I would take the job on if asked and I would point out that it will take at least a day and at my rate that is quite a lot of lolly.
On the other hand, you can have one of these nice four port APU4 based boxes running pfSense, that I can have up and running inside two hours. I keep a stock of them and will have your config backed up and to hand and can replace it within a drive plus 30 mins, if it fails.
If you want a CARP (VRRP) clustered jobbie and have a suitable WAN, I can do that too - all for less than trying to wedge a new OS on your ancient hardware.
"Thanks" to the pandemic I have a black belt in VPNs, routing, RADIUS, VoIP and all the other paraphernalia of remote working. At one point during the pandemic, I had the WAN at Kingston Comms emulated in my dining room (IPv4 and 6) so I could set up a customer system from Hull - a pair of Fortinets with thirty odd VLANs on the inside, rather a lot of IPSEC tunnels and a lot of port forwards. I have consumer grade Netgears at home so I couldn't use a CLI to magic loads of VLANs etc, so a lot of clicking ensued. I even used IPv6 NPT, some fancy footwork and a couple of tiny VMs on my home ESXi to emulate their external facing web gear. Obviously, I whipped up a DNS server with split horizon to emulate the internal and external facing experience. I might have gone a bit far at times but whilst everyone else was learning how to bake soda bread, I was doing my job 8) I also colour coded all the Forti firewall rules and the NAT related stuff (it's a right old palava on a Forti). It looked sodding complicated, yet logical by the time I finished it.
It took me two weeks to setup and test. I shipped them oop North (I'm in Somerset) with an excruciatingly detailed set of wiring instructions and photos and spreadsheets, and they fitted them and cracked on.
That's how professionals operate, in my opinion. You don't take the piss out of the customer - you cost up their request and offer an alternative that might work better and be more cost effective