Guest Wireless Network

I recently purchased a R4S router and installed OpenWRT on it plus added two RE603x access points hardwired to my to network via a few TRENDnet unmanaged switches. After doing all of this, I realized that I can't figure out how/if I can setup a guest wifi network using the equipment that I have and was hoping someone from this forum may have some suggestions.

After doing some research, I think I either need to purchased a managed switch or repurpose an old router and use it like a managed switch. Are there any options that I'm not thinking of?

If the idea is to use vlans from the R4S and extend them to the APs, then you need either managed switch or some repurposed router. Or you could connect them in a daisy-chain internet-r4s-re603x-re603x