What to shoot for the first time?

My first object was the orion nebular. It looked, well, shit… but I got an instant reward and learned how much actually is possible. I used a APS-C Sensor on a 400mm scope, so I got a bit more magnification, but your setup should be fine too. There are a lot of nice nebular in this region and a wider field of view is nice there. Tools like Stellarium can show you how your FOV is when you put in your camera/scope data.

Depending on where you live, it might take some month to get higher up in the sky. It's more of a winter object, but maybe you keep it in your mind. 

Clear Skies :-)

I almost always recommend Andromeda (M31) when someone asks for their first ever target. It doesn't really matter your equipment at all, as long as your location is somewhere that you can see it. It's big, bright, and forgiving enough for people even with just a tripod and no tracker to take a shot at. Then if you stick with it, it's one of those that are easy to come back to a year or two down the line and really compare your progress.

You can do some amazing imaging with that setup.  Pick any of those recommended targets, and go to work on it.  My first were with a canon, 200mm lens and a tripod.  I was able to image all of the ones listed above.  They improved greatly when i got a tracker.  Then, I got a full blown goto mount.  Then a telescope.  Then a cooled astrocam.  With each step, my images got better, but they all started with those first ones.

you just have to get out there and get started.  Good luck and clear skies.

I also think Andromeda is a rewarding starting point. You will allways get something to impress your friends. It's another galaxy!

M33 is a nice alternative if tou want to stray a tiny bit more out of the beaten path.

Multiple shorter shots is the way to go, in general. Especially with a ‘simple’ tracker like the iOptron, which does not let you correct the movement as a normal equitorial mount would. I hope you have a remote control for your DSLR which lets you take multiple shots, they come in very handy on those cold, long nights.

As for software to stack those multiple shots, there is plenty out there that doesn’t cost too much like DSS or Siril, no need yet to invest in stuff like PixInsight or Astropixelprocessor. Having said that, Astropixelprocessor is very easy to use and I never regretted buying it. 

Darks, flats, dark flats and bias calibration shots is a whole chapter by itself, and you do want to take these, as they will improve the quality of your images. Somebody already mentioned Astrobackyard, it is a great place to start to learn if you start out like you do now, and you can find a good explanation and a ‘how-to’ for these calibration frames.

Many short images (under 1 minute) and stack. Follow a youtube tutorial for DeepSkyStacker or Siril or ASTAP to stack your images (all free). You can stack without calibration at first. It won't be as good but it will make an image. GIMP is a free image editing app you can use with the above free software if you don't have (or want) Photoshop or Affinity. Now, on to calibration frames (optional at first but necessary as you advance)

With your setup, flats will be most important, darks and biases can come later but will improve your shots.

At the end of an imaging session, leave all of your settings the same (image length, iso etc) put the lens cap on and shoot 10-15 more images.  These are darks.

Leave your lens cap on and set your exposure time to 1/4000 or 1/8000. Everything else the same. Shoot another 10-15 frames. These are your Biases.

Take off your lens cap, switch to Av (Aperture priority mode) and hold an iPad with a white screen or some other even light (many people use a t-shirt over the lens and the early evening or morning sky). Shoot another 10-15 frames. These are flats.

Both DSS and Siril (and other many other programs) can use these calibration frames and they will improve your images but you can still get something to work with without them, so like Mathew says, go shoot, make many mistakes and a few messes and learn. Don't get discouraged. My first shots were messy, out of focus, off target, bad or no calibration and on and on. But every attempt improved something. AP is fun because it is difficult.

Astro Backyard and Nebula Photos both cover using basic equipment and early processing on their YouTube channels.