I used to run track in high-school and in CC. It's been about 8 or 9 ueara since I've ran in a track meet and 4 years since I've last ran (around Lake Merritt in Norcal) now that I've stumbled across your page the fire that was once out now has a small spark.
Bro without hate, your 800m warmup is ridiculous, at least run 3K or 2miles WU before dynamic stretching etc. You will increase your mileage easily and it’s important to have your body warm
Take your long runs now seriously, slowly keep making your long runs longer until you can run an hour without stopping. Then run that hour faster and faster every time you do it (about weekly). Your legs definitely should hurt later in the race if you're running a good pace 👍
Short runs at your 5k target pace mixed with long easy runs. On your longer runs you could start off with doing run/walk splits and decrease the walking time as you get more comfortable.
Before the marines when I was in hs and I was tryna get my mileage up. Only thing I did was run 1.5 miles for like 2 weeks or 1 mile if your really dying. But every 2 weeks I’d just add .50. Once you get to the point where u learn how to control your breath things become semi easy. After u get used to 3 miles it pretty much all mental from there