Running

Dieting is probably the most efficient method for weight loss.

I wouldn't focus so much on what zone you're heart rate is at. Consistency is key. Just go at a pace you feel is sustainable without burning yourself out in a couple weeks.

Trainers have the experience to know how much your body can take without getting injured, so in that sense they can provide you with a custom workout plan to give you the fastest results.

I could be wrong and I hope someone will correct me if I am, but my understanding is that the only reason Z2 training is recommended comes down to the ability to train for longer and to recover faster before your next training session.

This means it's much, much more relevant for professionals doing 10+ hours per week then it is for casuals running maybe 2 or 3, if that. They do it so they can still get the benefits of more running, but be fully recovered to get maximum performance out of their smaller number of Z4/5 sessions.

If you aren't doing high intensity sessions like fast intervals or hill reps, but are instead doing all your runs at the same intensity, then making that intensity the highest you can (without injuring yourself) is probably optimal within those constraints. And Z3 encompasses that level of effort perfectly.

I'm not saying, by the way, that doing only Z3 is optimal for amateurs. Especially if you go up to 3 runs per week I think making one of those a higher intensity and then dropping the others down is probably even better. (My basic running pattern when I want a block of thoughtless training is a Sunday long run of 60ish minutes, a Tuesday high intensity interval session, and a Thursday slow, easy 40 mins.) But with just two 45 min sessions, and if you don't want to incorporate intervals or increase the complexity of your training too much, Z3 is great.

Oh just a quick word regarding the other points. I agree with the other user. Running, like any exercise, should be about fitness and feeling good. Weight loss can be another thing that helps you feel good and get healthy, but exercise itself is not great for weight loss. Your body naturally tells you to eat more after exercise leading to neutral or even gained weight, if you don't accompany it with good diet.

If you don't want to talk to the trainers at the gym, there might be someone at a local running club, or an online professional coach you could talk to. I can't help you with vetting them or knowing how to talk to them though, I've never done it.

Being nervous and tense is normal. I get it all the time before a race, even after having started in many races, often even before shorter just-for-fun races. When the starting signal sounds, the nervousness immediately falls away, and your head will get into it, don't worry. :)

I've run three halfs in the last year. Biggest thing for me is focusing on my stride in the second half. As your legs start to weaken, your stride will suffer which may leave you at risk of an awkward step that could have you dealing with rehab in the weeks after the run. For me personally, a single odd step (imagine going down stairs and thinking there's one more at the bottom when there's not) has sidelined my training for almost two months now. I can still run, but I can't push distance at all. It's to the point where I'm considering another couple weeks off even after a month with no running after the half.

Keep your eyes on the upcoming terrain and make sure it doesn't surprise you.

I've not ever done one, but I guess remember that you're doing it for yourself. Just completing it will be an achievement in itself. Good luck and remember to have fun.

How did you go?

I use Alltrails and they cover Germany, from what I've seen an easy hiking trail is a good choice for running in general.

I know several people in Germany who are regular Komoot users.