DMX is a standardized language. That means that your DMX Operator will work with ANY brand of lighting hardware(fixtures) that utilize DMX, be it something as simple as dimmer packs, to something more "cool" like a moving head fixture.
The statement of "maximum of 16 channels per unit" is not entirely true, but really, if you don't follow that guideline, you may run into a good may issues trying to program fixtures that use more than 16 channels. Just don't do it.
You also have another issue to concern yourself about, which the manual tells you about. Your controller can only access DMX channels 1-192, so you don't get the full 512 channels. Considering this is a basic controller, if you really need more than that many channels, I would suggest a bigger controller or perhaps MyDMX software.
The DMX Operator is a great controller. I have one myself and even though I'm moving onto MyDMX, my DMX Operator will always come to shows with me. I've had mine 7 years now and am still learning it. For a basic controller, this does have a lot of stuff crammed in there.
As far as DMX Terminators, you SHOULD use one. It's simple to make, you cam make it out of a male XLR connector and a 120-ohm 1/4-watt resister soldered between pins 2 and 3. Should take about 5 minutes and cost less than $5 to make. I bought 100 of these resistors for like a $1.25, since they didn't sell them in smaller amounts. Plug your terminator into the DMX OUT of the last unit on the chain.
ALSO, it is HIGHLY recommended to use DMX cabling, which when using 3-wire DMX, looks and is wired exactly the same as XLR cabling.
In my case, my run from my mix position to the stage is 200-feet, so right there I know I ideally need to use a terminator, and I haven't done anything yet. Add cables adds length. While I have NOT had any issues without using a terminator, I make it standard practice now to use a terminator.
I also suggest that you make a few DMX terminators as they get lost easily. Mark it with what it is and your name, and if you're using connectors with a rubber or plastic strain relief cover, stick a short bit of tie line in there to make the terminator larger to help prevent loss. Maybe put loop in the end so you can attach it to a carbiner or something to make it easy to take back.
Enjoy. Great controller purchase, you'll love it for a long, long time.