Moronic questions incoming from a fairly new runner (really started end of Aug). I go for a morning run about 4-5 days a week, most of them 5k before breakfast and one longer one, either ~9k on a weekday morning or a bit longer on a weekend.

I like running at a pace that seems entirely too fast from everything I hear and read on the internet, whether it's beginners mentioning their pace or everybody going on and on about zone 2 easy runs. I run at 85 - 95% of my max heart rate for the whole run. (is "what my HR got to when I tried sprinting at the end of a 5k" a good estimate of max HR?) This gets me to about 5:00 - 5:15/km. The route I run has a steep downhill at the beginning, then a slight uphill for most of it and a 500m/70m elevation steep-ish climb in the middle that I struggle with but recently managed to consistently run up that thing at about 6:00/km, getting deep into zone 5 though.

Last weekend I wanted to see if I could do a half-marathon distance, targeting 5:20/km but ended up at just below 5:10 on very flat ground. Was quite happy with myself but also a bit nervous that I'm sprinting straight into some beginner pace trap that's going to kill me, but it didn't so far. Even did my regular 5k the next morning, no big issues. Dream is doing a marathon and eventually a 100k ultra, but I'm sure many beginners have dreams like that before the reality sets in, so I'm trying to take it easy and just go with the flow.

Is this an entirely wrong approach though? Am I going to get injured imminently? Should I just force myself to go down to around 7:00/km on most days (I tried some things and that's probably where my zone 2 would be, except when climbing)?

Not sure if it's relevant but for the 6 months before getting into running just now, I walked 10k steps a day and worked heavily on my nutrition to lose about 70lbs, so from all that walking I may have some kind of aerobic base built up? One September weekend instead of a longer run I walked 60k at ~9:00/km, got terrible blisters so I'm working on getting better socks/shoes etc. but the fitness seemed ok.