I'm with everyone else on the run/walk front. As to speed for running you should be able to hold a conversation when you're running. This should help you to gauge your pace more eaily.
As to the comments you experienced they were totally out of order. Parkrun is about getting everyone to run and there is no place for comments like that. Use it positively though to give you more determination to carry on and improve. |The majority of runners are supportive and will encourage each other.
When I bought my Garmin the TomTom multisport that was on the market did not support open water swimming, this is the reason I chose the Garmin. I cannot comment on how good the TomTom is though as I have never used one.
We all have bad runs, those runs where we just struggle to get to the end or give up part way through. The first thing you need to do is congratulate yourself for doing the run in the first place, a bad run is way better than no run! Things like this usually happen for a reason maybe (despite) following the plan you have overdone it? These plans whilst good are a one size fits all approach, perhaps you need to go back a couple of weeks and build back up again. Have you thought about running outside? I personally find it so much easier and more enjoyable.
These set backs do happen but it is how you overcome them that makes you a better runner. For instance I used to regularly run up to 13 miles, since a pregnancy related injury I was really pleased to do 5 miles yesterday! You just have to adjust the plan to you. Keep at it, you're doing great! Good luck with it!