Many of these cheap wrist heart rate monitors can be inaccurate. Especially while running, and more movement in your arms etc.
Also any of these 'rules' for calculating heart rate can be inaccurate. Presumably you have just done 220-age? That mostly works as an average, but some people have much higher max heart rates than that, some have lower. Doesn't necessarily mean you are healthy or not.
I have a chest monitor somewhere I can use for comparison. It's certainly accurate at lower heart rates.
Yes, all I've done regarding max rate is the 220-age thing. I wouldn't know how to judge otherwise.
Something else which may be relevant is that my heart returns to its normal resting rate (about 60) in a minute or so.
As Fuaran says, max HR is individual and the average isn't really much use to be honest. The point about max HR is that it is as fast as your heart will beat - you cannot exceed it. So (not medical advice!) don't worry too much about it.
If you want to monitor heart rate while running, a chest strap and watch is the best solution, but the recent Garmin watches do pretty well with their wrist sensors and monitor HR through the day too. I have a 935 which I usually, but not always, use with a chest strap for running and wear all day as a tracker. It tells the time too:) My old 235 was also a nice watch and now graces the wrist of one of our compatriots on here.
I really like the Couch to 5k plan, but be aware that it is too fast for some people. Be happy to repeat weeks and build up more slowly if you feel like it. Running less is better than sitting at home nursing an injury.
I'm not sure you need a gait analysis at this point. You will likely find that your feet and legs are weak from not running for years and carrying more weight than desirable. But you're not going to run far for a fair few weeks and the research suggests that shoes that are comfy to run in are the best ones to wear. Plus, by building up slowly enough to let your body adapt in terms of strength and bone density etc, you may either avoid injury altogether or find that your biomechanics evolve into wanting something different after a while anyway. I'd look for some nice stable, but not overly corrective, shoes and see how it goes. Listen to your body and learn when things are more than just a bit of carried over fatigue. Unless your willing to progress really really slowly with a higher risk of achilles injury, I would avoid any barefoot or minimalist shoes at this point - but habitually walking around the house and garden barefoot is good;)
Most of all, enjoy it. And take care of the ticker