UPDATE: I went ahead and tried doing it the route-nopull way instead. Had some success!
I added the route-nopull command to the OVPN client config. This leaves my routing intact, I think. Then I added this OVPN client connection as an interface, named it "VPN". This made the VPN appear under "Gateways", but the default is still my usual ISP on WAN. I then under "Outbound NAT", I removed all the rules, switched to automatic, saved, and then back to manual and saved. This created a number of rules apparently needed for this to work. Applied the changes.
Then I created rules for interfaces LAN, WIFI1, WIFI2. For all interfaces, I added three rules at the top that tells any traffic that has destination LAN, WIFI2, and WIFI2 to use default gateway (*). For LAN and WIFI1 I then added a fourth rule at the bottom for any traffic with any destination to use the VPN gateway instead. So everything that isn't headed for LAN, WIFI1 or WIFI2 will go through the VPN instead. For WIFI2 I just set the fourth any rule to go through the default gateway (*), so that one goes through my usual internet connection.
This actually worked!
The downside is that for some reason, this causes the CPU use of the pfsense machine to be at around 50% at IDLE. Load is 3,5-ish. This is without any heavy traffic over the VPN. When I use the VPN normally (before doing these latest changes), like downloading at 1 MB/s, I certainly see an increase in CPU use (like 20-30%) due to the encryption going on, but now it is constantly there instead. Very strange.
Also, one machine is connected to IRC, and that connection drops frequently (start lagging, and then reconnects) after these last changes.
Any ideas? Maybe I've done some configuration wrong, but what I don't get is what's causing all this CPU use.
EDIT: Something strange is definitely going on. When downloading, general speed to the internet slows down in a way that it doesn't normally do. Also, when I look under Status->Gateways, the VPN-gateway shows as Offline while the WAN-gateway is Online. The VPN still works for all interfaces using it, though...
EDIT2: Download speeds are also very unstable, varying between 50-1000 kb/s for the same torrent over time. Distinctly different behavior from before my latest changes.
EDIT3: Now I got a message in pfsense that something crashed (something with PHP..), and after that CPU use normalized. Download speeds are still going up and down like crazy though. Torrents sometime stop downloading completely for 5 min and then go up to 1 MB/s again.
EDIT4: I think I got rid of the problem with losing internet access. I disabled flushing of states when a gateway goes down. Seems like when I saturated the connection, "apinger" (or whatever it's called) couldn't ping my WAN gateway so it flushed states, making the connection go down for a couple of minutes. WHY this started happening with my new conf, I have no idea..