Garmin or wahoo

Choose whatever is familiar to you and will likely not cause you problems and gives you the information that you have used in training to determine your pacing.

If you are going to pace by heart-rate, then you need to know that.  Nothing else.  Ditto for power.  Pacing by time is generally a bad idea, but if that's your thing, then you just need time.

Don't overwhelm yourself with data during the race.  Focus on the one thing that you are going to use for pacing.  Practice using that one thing during training.  Use it, and nothing else, during racing. 

(If that one thing is rate of perceived effort, then you can ditch the computer stuff.)