Questions about ER-X-SFP

Hi All,

I´m thinking about setting up a simple network with a ER-X-SFP and two UNIFI-AP-AC-LITE, so here are my questions:

1) will I be able to have both APs on the same lan-segment (Vlan 1 or whatever) and an extra vlan on some other port without loosing forrwarding capacity in the router?

2) I have read about other ER models that have the operating system on a USB-stick, is the ER-X-SFP build in a similar fashion? If yes, is it a common problem that it fails?

3) Are there any problems with port failures in the ER-X-SFP, I have read that it can be a common problen on other models.

4) Is the firewall feature in the ER-X-SFP functional?

thanks  

/HZ