Congrats on your new house!

You're right about digging up that plastic. You can't garden until it's removed. Is there a border/barrier separating lawn from bed? If not, that would be my first order of business, installing one.

After removing the plastic, smoothing things out a bit, an inch or two of compost would be great. Top off with fresh mulch (3-4".) I don't think I'd bother with many, if any, really small plants this year for 2 reasons. First, they are the accessories which should be added after whatever trees and shrubs you want have been placed. Second, with all of the disturbance you are about to do, the soil layers need time to readjust to their proper levels, I'm a firm believer in letting the microbes and soil dwelling critters do their thing. Tiny roots of tiny plants might not find this a good situation this year, but shrubs or baby trees would have much bigger root balls that would be installed more deeply. Sitting potted plants on top of the mulch is a good way to have some flowers this year while the bed is recovering from the digging.

How much gravel is in there? I don't think I'd bother with trying to remove it unless it's more rock than dirt. The gravel likely won't bother whatever plants you want there later, it's perfectly normal for rocks to be in soil.

If you have a pic (or several) you could add to the discussion, that always helps the advice to be as specific and relevant as possible. You can add one pic per post, so make several posts if you have several pics.

If it makes you feel better, I'd much prefer to move to a house like this than one with beautiful landscaping that didn't necessarily suit my tastes. A basically blank slate is always more fun, IMHO.