building wifi point to multipoint

I want to transmit a wifi signal from my small business office to three rental homes. My office is located at the low point (50-100ft) below the three rental homes. The longest distance would be at most 650 yards.

The location of the retal homes falls just outside a 90 degree azimuth. Line of sight will only be an issue with the most remotely located house. There is a small finger of trees, 75 yds wide, that intersects our line of sight.

I am somewhat tech savvy however this is my first venture into the wifi field. Right now I am looking at buying a new router with the ability to interchange the antenna and replacing it with an 15dbi omni directional antenna to mount on the roof of the office.

I would appricate any advice I could recive on building a system top to bottom, what I am doing wrong so far, is it possible, ballpark expense from start to finish, who offers quality equipment. Any advice at all would be greatly appricated. Assume I am an idiot becuase I am so don't be afraid to go into too much detail or link me to another site for basics.

Do you have a clear line of sight from office to all three locations.

As you will be a facilities provider, you will have to file your FCC/FBI CALEA statement and the twice a year FCC form.

I have clear line of sight to two of the houses both within 275 yards. The third has a small patch of timber, 75 yards wide, intersecting my line of sight with the third that is 650 yards away.

Thank you, WHT, for your consideration, as I said I greatly appricate help of any kind.

Really need an aerial picture of this. Bing maps or Google Earth maps.

I ran a nail through my foot so I have had a lot of time to research lately. What do you think about a Wireless Mesh Network. The Gateway is marked(yellow pen most extreme left point) and the longest distance is only about 500 yards but I want to over build, overkill is underrated. I have clear line of sight from node to node with the exception of the gateway to the fartherest house. Otherwise ignore the trees as they are trimmed high enough to allow a clear line of sight. What do you think about a long range Wireless Mesh?

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Mesh works if you have compelling reasons and fully understand it. 90% of the people don't have those compelling reasons and neither understand it.