Struggling with prioritizing in my new neglected garden

Hi I inherited a small piece of land that has been neglected for the last 30 years. I’d love to permaculture it, but the issues are a bit overwhelming. I don’t know where to start.

There are 8 pear and apple trees of about 15 meter height. They shade a lot and cause a mess of rotten fruit on the ground. One seems like a good juice tree and 2 have amazing tasting apples on them. Others taste meh.

One side of property is covered in wolfsbane, another with old rasberries and some sort of wild plum. There are low areas that cause flooding during heavy rain. The soil seems depleted in many areas, compacted and heavy in clay.

And the entire property is full of invasive spanish slugs. The neighbors are stressing me out complaining about the slugs coming from my property to their barren lawn plots.

Good things: very nice east-south facing land, an old greenhouse, deep well, rich soil under the fruit trees, a river next to it and quite a lot of small wildlife and bugs.

Any advice on where to start and what to prioritize so I can prepare for the next spring? Need to get the land into managable shape and growing food.