We have 4x8 foot beds too.

I would broadly group plants into four categories:

• Things that stay low to the ground and don't spread much. Examples include carrots, onions, lettuce, etc. You can plant these fairly densely
• Things that climb (climbing beans, cucumbers, beans, squash, melons, peas, etc) or at least grow mostly vertically like indeterminate tomatoes. You can plant these somewhat densely. We tend to have one bed that has an 8' row of carrots, an 8' row of climbing peas and pole beans , a double/triple row of onions, an 8' row of indeterminate tomatoes spaced every 20" or so in a Florida weave, and another 8' row of carrots
• Things that are more bush shape, but aren't that unwieldy. Easy examples are bell peppers, broccoli/cauliflower, cabbage, and egg plant. We will plant eight of these per 4x8 bed
• Things that sprawl. These get their own half a bed, which means we don't grow them all that often. Examples include non-climbing squash/melon, non-climbing cucumbers, etc

There is a little opportunity for hybridization by putting something that sprawls in a bed with something that climbs where the climbing structure is on one of the sides of the bed. If you want to try a busy bed, I would avoid things that sprawl.

Chaos gardening to the max. Let it rip and see what you get. Learn from this years harvest and tweak next year

Thanks for everyone's advice. Here's some pictures of my bed for reference:

So, it is a bit too cramped. You probably want at least 18" at a minimum for tomato plants, and you'll also need space for cages.

Then you have cucumbers and gourds, which sprawl A LOT. That many in that small a space will quickly take over the entire garden bed. You can make the cucumbers climb a support of some sort, but not the squash and zucchini.

The other issue is the ground clearance between the topsoil and your drainage material. 12" isn't very deep, so you'll need plants that can root deep and easily move past objects. Carrots won't do that.

I'd take one of these rows out at a minimum. Maybe do the herbs in containers, maybe the marigolds in a planter just sitting nearby. You might have enough room for one zucchini on the edge of the bed, but definitely not the squash.

Another thing to consider: do you have rabbits and squirrels in the area?