Assistance Required With Redoing Entire Network

hire a pro.

As stated above - For that type of advice i would have a chat with a professional company, maybe you can get some freebies off them? - The two issues which you have correctly identified are backwards compatability and topology.

CAT6 E will most likley work on all machines, but you will not be runnig at full speed as it depends on what hardware is in the machines.

If you want reliable, don't use duh-link. Go with a better brand. For a small network like this, that has moderate network demands (e.g. not moving huge data) I'd look at a low end un-managed switch like a Cisco SG102-24 and a Cisco RV180W-A-K9-NA gigabit VPN router. This router supports IPSec, PPTP, and QuickVPN so you could easily connect remote users and offices securly if needed.

As far as the wiring is concerned, definitely CAT6, and use all CAT6 certified accessories (e.g. jacks, patch panel, etc). If space permits, you need to pull and terminate this to a patch panel to simply modifications in the future.

Elaborating on what has already been mentioned about hardware... Make sure your workstations are suitably equipped. No point installing CAT6e with GB routers, switches etc when your workstations only have 10/100 network cards.

This isn't a complex network and the easiest option I see is getting a large switch to place next to the Server and run everything back to it. I would get a 16-Port unmanaged gigabit switch along with several 8-port switches to split up the workstations. Something like this (Can you tell I'm not a graphic designer?)


Red lines = CAT6 Cable

The reason for 8-port switches where you could get away with 4-port is to accommodate future upgrades plus you may have network printers or phones that require ports.

Patch panel is optional but it does keep things a lot tidier and makes future changes/upgrades much easier.

This should give you a basic idea to work from. Remember this is just a guideline and you need to adapt it yourself. You could split it up into less or more workstations per switch, or you could even run an individual cable for each workstation back to a 24-port switch.

PS.
I missed out the WiFi as I don't know what you have.

Elaborating on what Casper1973 added, it's generally best practice to avoid chaining unmanaged switches when it's not necessary. In large scale IT, we never do that. Ideally, you'd home run all workstations to a central patch panel and use a single switch. With an office of this size, there's no real reason to run several small switches. The only real reason would be to save cost of cabling and the cost a single large switch (which isn't that much, honestly). Of course, there's no footage scale on the drawing, but it appears that none of your runs would be in excess of 330' (the maximum length for CAT6). I see 5 switches cobbled together in that diagram, where one 24 port switch would suffice. It also makes support easier. In the proposed diagram, you have several points of failure. One switch in the chain could cause everything downstream to also go down in the event of a problem. I'd still recommend going with a 24 port switch and pulling all runs back to a central patch panel, and all gear could be patched over at one point.

Agreed. Running everything back to one patch panel and then into a 24-port switch is the best option from a technical point of view. My decision to use small switches was based on ease of setup and lower costs. Running 4-5 cables as opposed to 15-16.

As I said previously, the diagram was only a guideline and I expect you to put your own spin on things. Something I would add in hindsight is a redundant cable to the 2nd floor. If that single cable were to be damaged you are in trouble.

For starters, I agree, if you want reliable, stay away from Dlink. Some folks seem to like them, but I have had nothing but disasterous results from their equipment over the years...

I would start off with a good DSL modem. I don't have DSL so I cannot recommend anything specific there, just get the best one you can...

Then...
#1. Get yourself a wall mount relay rack, at least 4u, and 10" deep. I went with a Monoprice 7u 12" deep rack, it is perfect for my network, but I also have a rack mounted KVM and switches for an iSCSI SAN, so there are 3u you won't be using, at least immediately.
#2. Top quality / fully featured router with gigabit ports. I personally like Buffalo, Asus, and Netgear. I have a Buffalo WZR-600DHP, if I couldn't have this router, I would probably go with an Asus N66U. If you go with a DD-WRT enabled router, I believe you can use channel bonding and uplink your LAN ports to your switch to dramatically improve your bandwidth to and from the router. (I haven't tried yet, haven't felt the need to...)
#3. Next use a good quality 16 port gigabit switch as a minimum, but 24 port will allow for expansion. The TrendNet TEG-S16Dg (16 port) and TEG-S24Dg (24 port) are excellent units for the money.
#4. I am too lazy to read all the responses, but cat 6a (not 6e) is the augmented variant of cat 6, and it is substantially more expensive than regular cat 6. Unless you have long runs (over 60 meters), regular cat6 will work with 10GBASETX just as well as 6a. So get and install a 24 port category 6 patch panel, and cat6 cable. Run your drops from this point. Use Category 6 rated keystones at the wall ends as well.

And yes, I understand it is a pain, however you are already running a few drops. The hard work of running a few versus running a lot is already done. The hardest part is getting up through the headers between floors.

The reasoning for this is the location of the server, versus the location of the majority of the worksations. If you were to take a single run to a switch per floor, you would simplify your installation, but performance would really suffer with so many clients sharing a single gigabit cable.

With this setup you will have maximum bandwidth available to each client and the server, the cabling would be capable of 10GBASETX, so would be reasonably future proof, or at least resistant, once the switches, NICs etc... come down enough in price to be used at the home / small business level. You would then be left with one weak link, and that is the DSL service. (I have 105/20 cable and sometimes I feel it is slow...). Not much you can do about that unless you are lucky enough to have Google Fiber in your neighborhood...