No experience with such a space, but your plans seem intelligent to me. And yes, All Sonos speakers can be grouped with each other.  Alexa controls the Sonos ‘system’, not a particular speaker, so you can control a ‘room’ using the microphone on another speaker, even if the ‘room’ doesn’t have a speaker with a microphone. 

As many Era-100s as you like, distributed evenly, set up as stereo pairs or as one big zone.  The choice of pairs or zone depends on if you want an overall sound with one volume (zone) or separate pockets of stereo sound (pairs)  in different areas with individual volume controls.

I don't recommend the Era-300 for that space.  Atmos is the only feature gained, and Atmos is dependent on a fixed listening position.

You can also review Sonos Zone setup here. However, with Sonos Zones you cannot add a sub. Below is a sneak peek at Sonos Zones

Set up a zone for multiple Sonos products

I’m not a fan of ‘zones’, they’re a commercial feature that escaped into the ‘regular’ world. There are some restrictions (such as, if memory serves, adding a Sub) that don’t sit well with me. Even with the amount of power interruptions I deal with on this location I live on, grouping once after each power outage just isn’t a big deal…and I never lose a ‘room’, just grouping of two or more rooms. 

I get that you're not a fan of zones and if not for the size of the OP’s space I wouldn’t have mentioned it. Just wanted to provide options.  However, I did mention that a sub can’t be added 😂. 

I'd start with a good quality surge suppressor on every Sonos regardless of what you get. Power tools can do rude things to power.

Initially I thought Sonos Amp and four high efficiency, large, bookshelf speakers mounted in the corners for maximum low frequency response. Add another Amp and more speakers at the mid-point of the walls if you needed more volume.

But if you liked the 100s then corner mounted to start with adding mid-wall ones if needed.

Try stereo Pairs and mono, pick what your ears like.

Add a Sub to an individual 100 or to a Pair, or Amp, maybe a second if needed. Again in corners for maximum impact.

Understood on the Era 300.  I’ll stick to just adding pairs of Era 100s.  Much more economical too.

I think this will be just a standalone “room” with no “zones”, so hopefully will be able to add a sub if bass is lacking once setup.

I think this will be just a standalone “room” with no “zones”, so hopefully will be able to add a sub if bass is lacking once setup.

I ran a TON of outlets in this space over many circuits.  One of the main considerations of the Sonos system is that I didn’t have to run wire to individual speakers.  The fact that they can all connect via WiFi is one of the benefits.  At least that’s the plan...

Not a Room but multiple Rooms, one per speaker or speaker Pair. 

You would Group* them together to fill the shop or just use some for local sound.

You can add a Sub to a single Room, be it one speaker or a Pair. It will alter the frequency response on the Room it is connncted to, not the other Rooms.

*You can create a Group shortcut for each arrangement you like or just select the speakers you want to Group.

Also, I ordered another pair of Era 100s so will be setting up four Era 100s in the corners tomorrow to start.  I’m hoping to use an Echo I have already which controls a receiver and a pair of B&W monitors (via aux cable) to control the Era’s.  I understand that they are separate so will not expect them to play in phase.

I’m hoping four Era 100s are a good start and will add two or four more along with a sub or two to finish it off.  

What does ‘in phase’ mean, to you? If they’re set up as either mono ‘rooms’ (one speaker), or stereo rooms (two speakers), they’ll still play in sync. It’s what Sonos (when grouped) is designed to do. 

Just FYI….

In an area as large as yours I suggest you starting thinking in terms of a “Space” that may have Multiple Rooms”.

As was suggested you may want to have a speaker in each corner and a pair in the center across from each other. If you want to control the speakers in the corners separately versus those in the center you’ll configure two Rooms in the same Space. 

One room might be named “Four Corners” the other named as “Center”.

You can then stream to either room individually or Group them together.

Grouping can be done on the fly or you can create a Group name or simply tap a Sonos pre-configured Group called “Everywhere”.

Learn about Grouping here or come back to the community for assistance 😊

The Sonos must be Grouped to play together, if not it wouldn't be a phase issue but each playing different music. Even if you try to start them together (not going to work) they will soon be playing sections of the track seconds apart or even different tracks from your source.

Trying to bring in a non-Sonos device will make that worse. 

Group all Sonos, maybe use your Echo for control if the Sonos options aren't working. 

I believe the OP was referring to phase/being out of sync between the receiver/B&W speakers and the Era 100s.

When I mentioned “in phase” I imagined I could play music on the echo which is connected to a receiver via an aux cable and pair of hardwired speakers, and then also extend to play on the “workshop” room of the Sonos speakers (however many I end up with). The “in phase” part was whatever delay there was between the hardwired output and the wireless feed to the Sonos. I’m not sure that simultaneous play is even possible. My four speakers should arrive overnight so I can set them up tomorrow morning and test them out. 
 

fingers crossed…

Ah. Every Sonos analog line in has that 75ms delay, which puts the Sonos system ‘out of phase’ with other speakers that aren’t also delayed. The best way to ‘fix’ that is to send the data to Sonos first, then play the output from the Sonos on all speakers. Of course, that requires a Sonos Port (or an older CONNECT). The Era 100 (all versions) has no outputs other than the speakers.

Honestly, you’re probably better off with just the Sonos devices, and forget non-Sonos speakers. 

How does the size and shape of your space compare to the auto shop that you like?

Keep in mind that the speed of sound is pokey at about one foot per millisecond. This means that the speaker at the far end of the space will be about 80ms out of sync. Unless you approach this system as if it is a music hall that probably uses a large speaker array at one end of the space, possibly with smaller speakers in the rear that incorporate a time offset, I recommend using multiple speakers along the long walls. Speakers every 10-15ft would allow you to be relatively close to a speaker that would dominate at your current position, minimizing the influence of more distant speakers. However, this cannot be perfect because the side walls are 50ft.

Another approach would use three speakers along each sidewall, separated by 50ft. Alternate left and right along the wall. SUB’s in corners will be most effective, but may not sound the best. You’ll need to experiment.

If you have an office area, consider using a local pair of speakers for that area.

All speakers in a Group will be time aligned with each other, but this cannot overcome the physics of pokey sound travel.