Tried the London Marathon sweatshop's running group for a 5k jaunt around shoreditch and dalston. NIce setup if you live or work that way - 'adidas 26rs' are funding them with free showers/changing room/stretch area etc.
The run was fun - I ended up chatting to a order (minor) trainig partner of Mo who was working back to fitness after a broken ankle. I say chatting - I was timing and choosing my worlds carefully and he was clearly at easy pace!
And some bloke came off his moped. At which point some fat bird shouted 'Daaaahn just stand verrrr - do summink!' then carried on eating her KFC.
He was OKish by the way. Lucky guy - just needed his moped wheeling to the roadside. Life imitating Eastenders.
The above is a fine prigram for someone who wants to cross train and be generally fit. something along those lines would probably work well for military fitness for example. However if you have that big a bias towards running goals at all distances you'd really need to de emphasise everything bar running to some extent. You'd need to build towards 3-4 runs a week With one of those being a long slow run.
You can certainly find a place for one weights session (though going heavy may give you too much soreness for hard running )
if you don't have major swimming goals then there's a place for that too especially if it's easy, recovery friendly swimming rather than hard interval sessions.
Gymnastics covers a lot. on the one hand the core strength and posture aspects complement running however the strain of it and risk of turning an ankle or jarring a knee etc don't sit well with long term running plans
id forget PBs for now and just build distance. your improved fitness will see your parkrun improve naturally