For your weather problem, Bienchen has a mod , a tweak to game's sunny lot trait, here:
https://deichschafblog.de/bienchen/jahreszeiten-seasons/ (scroll down quite a bit)
lottraitsunnyaspecttweak
The lot trait sunny aspect now guarantees sunny weather for at least 24 hours after (re)entering a lot. Even without the lot trait, it will no longer rain during romance, humor and jinks and nerd festival.
If the park is not available in events menu, have you tried to change the lot type of the park to something else? (I haven't ever tried to hold weddings at regular park, so I have no idea should it even show up in venue list)
