Why do I need a switch?

Only when you add more digital stuff into the signal path can you add the highly desired pixel dust. It makes the zeros rounder and the ones straighter. 

I actually do use a switch, but could care less about the audiophile tweaks. I have 5 devices in my HT that need Ethernet. I have a 50' run from my Wifi router to the outlet at the entertainment center which goes to a cheap 1 gbit switch to feed all 5 devices. 

I keep the switch power supply on the "dirty" side of my power conditioners.

I do use a hospital grade Ethernet isolator immediately before that switch, but its’ a surge thing. If lightning were to come down the 50’ from my router it would take out a lot of gear.

My internet provider is MetroNet. They use fiber optic cable. Wouldn’t my best option be to run fiber optic from the modem to the streamer?

Now Switch.

To your question, you don't need a switch, and you don't need fiber.  The signal is the signal, so that doesn't change.  The starting point is to connect your Ethernet cable to your streamer and listen to music. From there, if you wish, you can explore the many products designed to "enhance" your digital music experience.  These products generally claim to either remove noise alleged to ride on the Ethernet cables, or to reclock the digital signal thus sending a signal with lower jitter to your DAC.  These range from different cables to switches, to filters, to reclockers, to digital-digital converters (DDC) that buffer and reclock the signal and also allow different formats of digital inputs and outputs.  

Switches can have clocks, such as the English Electric 8 and Bonn Silent Angel N8 switches discussed in this thread, which are both essentially the same switch from the small OEM manufacturer ThunderData, in Guangdong, China company.  They both have the same board inside and both have an added TCXO clock.  My understanding is that the English Electric switch has a fancier case and feet.  There are even more expensive switches you can purchase with one of the top-of-the-line switches being the M12 SWITCH GOLD, by JCAT, for €3,800.  Silent Angel has a Bonn N8 Pro switch, which is supposedly better for audio (BTW, the new fad is to put "PRO" behind a product's name to indicate an upgraded, better quality, and more expensive model).  Here is an article about switches from two years ago.

Regarding fiber, that is simply a method of providing optical isolation for the purpose of reducing noise.  As stated in this thread, you can do that with two $25 converters and inexpensive fiber cable.  However, be aware you are adding two noisy SMPSs with those converters, unless you also splurge for a couple of LPSs at around $100 each.  You can also do it by using the GigaFOILv4, which would require only one LPS.  I have both the fiber/converter set-up, and the GigaFoilv4, and I have tried both, including the LPSs.  My run is 45 feet from my router to my system and I have both CAT8 Ethernet and fiber cables permanently in-place, so I have conveniently tried A/B comparisons between the two over a longish period.  I seem to detect a slight difference in the sound but ended up prefering the CAT8, at least with my current set-up, although YMMV.

Whether any of this changes the sound of your system, only you can decide and, unfortunately, only by listening, not by reading these forums which are great for learning what is out there but not so great for evaluating the actual sonic impact of this stuff.   In my system, none of it makes a profound difference but maybe a little so I am using a bunch of stuff, nonetheless.  IME the components you are using (i.e., streamer and DAC) have a much greater impact on the sound than cables or add-ons.  Below are the ancillaries I am using:

• LPS on both modem and router
• 45' of CAT8 into dual Bonn N8 switches with two LPSs
• muon network cable/muon filter into server
• muon USB cable into DENAFRIPS Hermes DDC
• TWL AES/EBU into DAC

Good luck.