Multiple Non GPS 2.4 AP deployment question

First some background.   I've been in telecom most of my adult life, and was involved in WISP deployments a lifetime and a half ago.  Ended up working mostly with the old Canopy systems in all the various spectrums, 

Flash forward to today and I currently live in a VERY small town with about 350 people, 75 miles from anywhere.   It's situated in the Arkansas river valley in a hole, i.e. pracitally no cell phone coverage, off the air television requires a 3 story pole with the the highest gain antenna and a 35 db booster. On the positive side, we are well protected from gamma radiation and EMP.....and WISPs

The town is currently served by junk DSL.  The provider is working to discontinue the service and refusing to turn up any new customers, leaving everyone with even junkier satellite as their only option.   I've convinced the small town, who had a VERY limited budget to create its own small WISP, primarily as a service to itself and to eventually generate a little revenue.   The speeds will range from basic access of 1.5 to 10 Meg, with unlimited usage.  Besides the low speeds and reliability issues of the DSL, the biggest complaint was the overage charges.   Most peoples bill often doubled, especially for gamers.

The town has a 90 foot witches hat water tower dating back to 1911.  Its been in continuous use and was standing when the Titanic sank.   Utilizing the walk space, it puts us about 75 feet off the ground....With the terrain, a valley, surrounded by ridges, we have a range of about 3 miles everything but 900 dies at that point, and 900 doesn't get much further.  Our furthest sub is on the old 900 FSK at about 5 miles.

The in towns customer base will probably never exceed 50 subs, with another 10 or 15 outside town within that 3 mile range.  

We originally deployed some old Canopy P10 advantage 5.7 and 900 gear we got for practially nothing, including the antennas.  (Probably enough scrap aluminum in the antennas to cover our purchase price).  We quickly realized the trees were a problem for the 5.7 and that with the modern throughput demands, the 900, as reliable as it is, simply isn't going to cut it.  

We have a lot of dense trees clusters in town so decided to avoid the 5 Ghz altogether and the new 900 isn't anywhere close to the budget, so chose the ePMP 1000 2.4, especially since the Spectrum is so clean here.  

As I mentioned earlier, the town has VERY limited funds and I've volunteered to oversee deployment.  Bandwidth isn't an issue since we have two fiber sources coming through town (and a 3rd just across the river).  We currently have a fiber feed in place with 100 meg, upgradeable to a Gig. with mulitple feeds available, delivered right to the tower.

As proof of concept, we deployed a single non GPS AP using the Cambium 90/120 sector with a 20 Mhz channel facing West and it worked great.  Wide open, I was getting 65 meg at my house about 1/4 miles away punching through several trees.  It wasn't full summer yet, but it was still impressive.  We began deploying and gamers were our first customers.   

We later added a 2nd non GPS AP using the same antenna facing South East with a 10 Mhz channel, separated by enough guard band that there appear to be no interference issues, and it also works great.  From the water tower position in the north east of town, these two antennas cover about 90 percent of the town.

People have been reluctant to give up their DSL since they know once they shut it off, it won't come back.  It's gone in early 2020 anyway, so we'll get them as a customer regardless.

People are slowly becoming convinced it works quite well.  We have yet to lose a customer during heavy rains, even with the trees.  Signal degrades of course, but nobody has dropped out yet.  The DSL crapped out with the first sprinkles.  We can offer higher speeds than their old DSL, without the drastic slow downs of an already slow service during peak times.

We have been approached by a nearby small sub division close to a nearby town about 3 miles way, which is on the "good side" of the ridge.  They have similar junk DSL from another carrier, that is down as much as its up, with horrible speeds, yada, yada and there are several potential customers we could reach.   We are looking to deploy a 3rd antenna on the north east side of the water town, appropriately spaced for the 90/120 sectors to reach them.   We are also exploring setting up a back haul to a rural water tower on the peak of the ridge west of town to provide coverage for customers over the ridge.  Not a huge amount, probably another 25 or so subs.  The backhaul would be easy as its clear LOS between the towers.

While we will eventually have to convert to GPS sync, we are just at the break even point, so throwing another 2K out to upgrade at this time won't fly.   Using the old logic of utilizing a guard band of twice your channel width, it looks like I could actually get away with 3 AP's using 10 Mhz channels at 2407, 3437, and 2467 and not interfere.  I've looked through many forum posts but don't see where anyone has mentioned actually doing that.    I do have the advantage that in addition to the Cambium sector antenna sides, the rear signal is going through a couple of inches of steel and a few thousand gallons of water.  

Playing with the systems early on, I can definately tell when interference is occuring, frame rates max out, prevously solid customers throughputs drop, etc.,  SNRs degrade, etc.   I'm cheating the GPS gods right now by running one AP in the 20 Mhz channel and the other in the 10 Mhz with plenty of guard band, and its running fine.  I'm not particularly worried about the normal background interference assosicated with the low-medium-high channels, because it simply isn't a problem here. Physical separation isn't an issue on this water tower.  We've got room for way more than we will deploy.   

We will get to GPS and 20 Mhz channels eventually as we want to offer 25 Meg in the future, but, until that day comes, is there any reason why I can't get away with running 3 non GPS AP's at 2407, 2437, and 2467 with 10 Mhz channels?   The needed 20 Mhz guard bands are there, but I know Canopy was proprietary and the Cambium has some of that as well, so......

Don't really want to go the 5 Mhz channel route due to the low throughput.  We are currently spiking in the low to mid 20 meg on both AP's at peak, and I want to be able to add more subs.

Any feedback is appreciated!

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Gps would allow you to run 4 20 mhz wide channels and you’ll be a lot better off performance wise. 

I know your asking about non gps, but it wouuld very much be worth the money. The guard bands you suggested will no help with coband noise when those radios get busy.    Gps will be your only fix for that. 

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I suspected as much.  I'll tell them they are just going to have to bite the bullet and cough up for the GPS.