|A quick google search tells me the Avaya ip office 500 is a phone system. I'm not interested in the details but whether VoIP or digital, if you want to have phones, I suspect you need it.|
A switch and router are pretty much necessary if you have need for more than 4 network connections. Your router is likely your gateway which provides your LAN clients access to the internet. Also, depending on it's capabilities it could be providing your DHCP as well as NAT. I hope it offers a firewall as well since that's always a good thing to have between you and any public network like the internet.
As to your internet bandwidth, what are you paying for from your provider? To check and see if you're getting what you're paying for, google "bandwidth speed test" and run 2 or 3 different ones. Compare the average to what you should be getting. If it's about 10 to 25% less, then you're getting what you're paying for. If it's less than 10 to 25% less, then call your ISP and ask them
From the sounds of it, you didn't set this all up. If you're not sure you're getting what you're paying for, or have more equipment than you need, may I suggest hiring another (qualified) consultant (who has experience and references in industry that you can check) to doublecheck and see. If whoever set you up ripped you off, you could always sue them and get your money back.
If you got your brother-in-law to set you up because he "knows all about this computer stuff" then you likely aren't setup correctly. If this is for a business you want to always hire qualified people with a business that's been around for a while and a reputation. Qualified people with a reputable business can offer you a list of satisfied customers you can call and ask about the consultant and the quality of their work and support. Yes, a qualified person is going to cost you money. But keep a couple things in mind.
1) You get what you pay for
2) Your brother-in-law who "knows about this computer stuff" isn't going to warranty his work.......if he even knows what he's doing
3) in Canada, where I live, money I pay a consultant to do work for my business is a tax deduction.
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.