|At the risk of being rude I must tell you, I won't do what you ask. A big part of the reason why is that it's impossible to do this properly over this forum. Also, we're here to help average people with problems that for the most part, are average. What you're asking for is a complex solution that's going to require quite a bit of work to put together. There is nothing "average" about your request.|
I understand you can't afford to have an IT department so the best advice I can give you is to contract this job out to a professional. If you hire a contractor, it's only for the one job, and their association with you ends at the end of said contract. A professional will turn over all documentation to you so that if you feel it necessary at some point in the future (and I promise you, it WILL become necessary at some point) to call in another professional to troubleshoot a problem, they will have all that documentation available to them. This will include setup information, hardware information and login information as well.
You might want to look into hiring a company that does this type of work. A lot of businesses out there will sign a longterm contract with you guaranteeing lower hourly rates for onsite work than if you don't sign a contract with them. Of course, this will involve and annual fee as well as the individual invoices for each onsite visit. I've worked for a company like this in the past and they had many clients like you whom I supported while employed by this company.
Based on the info you've already given I'd estimate (conservatively) 100 man hours to do this project. This includes planning, research & purchasing of equipment, configuration, testing, and finally, deployment. This does not include the cost of hardware.
This of course are just an estimate off the top of my head. To get a truly accurate estimate would require a much more in-depth analysis of the project's requirements. This is why I'm recommending you tender this out to several contractors/companies. I highly recommend doing some serious research into each before signing anything so as to avoid the fly-by-night people/outfits, of which there are many.
You're going to want/need an experience professional who has the right qualificiations and experience who's done this type of job before and guarantees their work.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.