Network help!

Hello everyone. I'm hoping to gain some insight on our small business network setup. To be fair, I am NOT a network expert, nor an IT professional, so if you are reading this and thinking to yourself, "this should be in r/'xyz', not here!" Please kindly direct me to the best place to re-post this.

Basically, our small business (10 room bed and breakfast) has recently upgraded from charter 60 meg service to charter's 1 gig service. We are experiencing some painfully slow speeds on devices, particularly over wifi, along with frequent "hiccups" on connections. I will describe our hardware setup as best I can here:

MODEM: Charter/Spectrum supplied E31U2V1 (modem only) ROUTER: Netgate SG-3100 WIFI: Eero gateways (3x) with ethernet connected from router into each gateway. Two of them are running through new unmanaged switches. Eeros are in bridge mode currently.

I realize that I am a newbie, and probably have some configuration issues going on that is at least contributing to the poor network performance. So let me explain my goals for the system, and if something obvious comes to mind, please let me know, so I may investigate.

We have three "offices" in the building where devices need to be hardwired, so there are a few unmanaged switches in the system. We also need wifi throughout the building for our guests. Given the hardware we have, how would an expert such as yourself set it all up? Do we need to ditch the Eero gateways in favor of enterprise access points? Do I need to use a dedicated wireless router in access point mode fed from the netgate router to feed the eero's?

Give me your worst, I am prepared to be called out on my lack of knowledge here, but I am trying to get an idea of what is mis-configured or just plain wrong in application. Any feedback is appreciated, thanks for your time!