WR840N-v2 with LAN bridge and wifi and another wifi isolated from the bridge

Installing and Using OpenWrt
1

I have a wr840n router.
This router will receive a DHCP network from a main server on the WAN port.
I need to configure it as a bridge on the LAN and WIRELESS ports.
Then I need to configure another WIRELESS network strip isolated from the bridged network.

2

This device isn't supported anymore (for half a decade by now), as it doesn't meet the hard minimum system requirements. For security reasons, it shouldn't be operated (in any capacity) anymore and would need to be replaced with something more powerfuk.

3

I understand.
This configuration I need will be for a short period of time until the equipment is replaced.