I would like to get some advice on HD video, cameras,camcorders, and operating systems

I also had an older Sony Camcorder. I replaced that with a Canon HFM50. I only film in AVCHD and I use Toast to burn blu ray quality DVD's using standard DVD discs. I also use iMovie but the quality is not as good as Toast. Canon also supplies some software that can be used on your Mac but I usually just use Toast. The camera uses an SD card that I usually remove and insert in my SD slot on my Mac to download the movie. I find this easier than trying to connect directly from the camera. The new 4K cameras are expensive and not sure you can see the difference on playback unless you also have 4K TV. I find my camera very easy to use and has more than enough features for my use.

Congratulations on coming over from the Dark Side. You must be stubborn. Doing video work on a PC for all those years must have involved a lot of suffering.

I have a Canon Vixia HF S200, not up at your level, but still shoots superb HD video. (So does my iPhone 6+, for that matter). The Canon was 500 bucks refurbished. I use it for family stuff, kids' recitals, and also for shooting some surgery video in the OR, which looks excellent, even after extensive cropping. OR video is difficult to get right, as the lighting is extreme, and the differences between different tissues can be subtle. The video looks incredibly good.

You will be very pleased with how well your Mac does video editing, compared to what a PC can do. The PCs that I use at work, and the windows OS, and the video editing apps on it, all appear to have been designed byretards. Simple and creative things that iMovie does easily and intuitively are a complete clusterf--- on the PC.

iMovie is perfect for me, and no other software is necessary.

I would make sure that your iMac has a lot of RAM and hopefully a SSD. I have 8 GB of RAM and a 500 gig SSD in my 2011 MacBook Pro (8,2) and it performs well. You will need to keep enough free space on your hard drive, like at least 10%, and perhaps more, like 20%.

SD card media is definitely the way to go. My Canon has two SD card slots and I have a 16GB card in each. I can shoot over an hour at the highest quality setting, and the Canon automatically makes the switch to record on the second SD card when the first one gets full. Extremely simple to transfer the video into my Mac, via the SD card slot.

I haven't burned anything to a DVD for years. Much simpler to store things on hard drives. If I want to share a video with family or friends, it can be posted to Youtube with a click or two in iMovie. If I want to watch something I've created, I'll watch it on my Mac, or stream it to a TV with Apple TV.

A few other suggestions:

Don't install any "cleaner" apps, like MacKeeper or CleanMyMac (which really should be called "TakeABigShitOnMyMac"). These are unnecessary and harmful on Macs.

Don't install any third-party "antivirus" software on your Mac. Unnecessary and can greatly impair your Mac's performance.

I mention these because they are popular with recent converts from the Dark Side. And they can screw up your Mac badly.

Welcome to the world of Mac. Some ‘light’ reading to help the transition. I don’t recommend trying to get through all of this at once.