@panosv
It would depend on the hardware you have available to do this, VLANs require the AP, Switch and Router to support the VLAN. This is generally not something that is possible with home grade hardware
Assuming that you have the hardware in place.
1. On your Switch and Router create a new VLAN, call it GUEST and set its ID for 123
2. Switch the WA801ND to MultiSSID mode and create a WiFi network called Guest, set the VLAN ID as 123. Traffic now on that SSID will flow via the VLAN 123 and not near your "personal" traffic
3. Lastly on the switch you can enable can Bandwidth Controls for that VLAN, set it for 10mbps down, 1mbps up or whatever you feel appropriate. This will indeed limit the bandwidth for you.
I have 4x vlans at home and use bandwidth controls on all of them, again via the switch. This is typically not something you want the AP doing
A quick hardware setup for this would be
1x OC200 Controller
1x TL-R605 Router
1x TL-SG2008P Switch
1x EAP225
That setup is based on Omada and would allow you to create as many VLANs as you wish, put bandwidth controls on them and even have a portal access for guests.