You might as well just get the MOS version and be done with it. It will give you more options too. Just looking around, it looks like its going to cost you the same $100+ to have a non MOS milled, and then you have to deal with all that.
Glock used to give you a number of different adapter plates, but now seems to have narrowed it down to the RMR plate. Others are available too, and other people are making them as well .
Holosun now has a series of sights (SCS_MOS) that mount directly to the Glock cut-out without an adapter plate. The sight is smaller, and sits lower, and you can use the factory iron sights with it, and don't have to buy suppressor height sights, assuming you want BUIS.
As far as the dots and their cost goes, I learned early on with my rifle dots, spend the money you don't have and get as good a sight as you can. It will pay for itself in the long run.
That said, if you arent sure and don't want to dump a lot of money into it, Id avoid the "cheapest" you can find and at least go middle of the road. Trijicon seems to more or less be the gold standard here, but Holosun seems to be gaining in reputation and the cost can be a couple of hundred cheaper, if not more.
I went with the Holosuns to see if it was something I wanted to do, and haven't had any issues with them, and I have one of gun that has over 5K rounds on it now. Battery life has been good, and they are easily accessed and changed if you need to. You don't have to remove the sight to replace the battery.
If you're going to mount the sight yourself, youre going to need a torque wrench/screwdriver in in/pds and the appropriate torx bits. They are easy to mount and zero, but you still need to do your homework.
Be prepared for a bit of a learning curve shooting with them too. They take a little getting used and figuring out, so don't get frustrated and give up too soon. The time and effort you put in will be well worth it, but it will take a little time. Dry fire is your friend here too. There are also several good videos on YouTube to help you out too.