That is great I always love it when people get into gardening. That excitement is always refreshing to see but I always want to see it be successful because in my experience new gardeners get discouraged easily and once they do they have a tendency to give up. So first things first I'm not trying to mean. I'm just giving advice from own experience.
Forget the vining crops in a raised bed this small. The time to maturity coupled with the limited space will make it hard. Even trellised the squash and cucumbers are going to be difficult.
Early crops like lettuce and onions are a great idea in a space like this but you need to sow the lettuce seed soon and get the onions planted now. They are cool weather crops that don't do so well once the late spring/early summer heat hits.
Not sure how you feel about radishes or snow peas but sowing the seeds now is the perfect time to do so but keep in mind it might be to late depending on were you are located.
Don't be afraid to remove them to make way for your other crops once the warmer weather comes.
Garlic is a fall crop. Don't plant it in your raised bed unless you are willing to allocate that space for at least a year.
Tomatoes and pepper plants get big. It's getting a little late to start them from seed but even if you buy starter plants make sure you give them enough space. The same goes for bush beans. Proper spacing is very important so make sure you keep that in mind with the new garden.
I understand this is your project and you want it to be the best it can be just keep in mind it is a limited space so don't try to pack to much into it at one time.
Last but not least have you considered buying a tractor and a tiller attachment? With all that space it seems like a shame to let it go to waste. I know you like big trees but you and I will be dead by the time they reach maturity....in the mean time you could have a killer garden.....just something to think about.
Thanks for the recommendations, I'm still not knowledgeable enough about what seasons are for what. We're still not done with freezing temps yet, so I'm hesitant to plant anything that cannot survive cold snaps. It's going to get down to 20 next Thursday and nothing's even really budding yet. I know a few of my seed packets do say to sow them before the last frost, so I'll be doing those as soon as I can get the last layer of dirt on.
We're honestly planning on like, one of each plant, not grouping of things. Just enough to get some fun veggies to compliment our dinners, not necessarily to survive off of. If a section of the garden goes to one tomato plant, we'll be thrilled with that. We had a bigass 6'x18'? or so in-ground garden that we tried last year that completely got out of hand... far too much work for us on top of everything else. We did get some nice onions/potatoes from that though (going to do potato bags this year).
As much as I like peppers, they're off the table for us. SO is allergic to the skins.
A tractor and tiller is well beyond the scope of what I'm looking to do (not to mention affordability), this is a side project, like my trees. I still have a 9-5 to keep up with, and if I can't weekend warrior it, it probably won't happen haha. If I wasn't lucky enough to be working remote right now this might not have even happened.
5 feet across is nothing. Veggies don't like to be packed together and you need some space to work around.
You probably can only do 2 kinds of veggies at most at one time and rotate between different seasons.
Garlic will take at least 9 months I guess? I'll start with spring onions (scallions) / lettuce that grow fast.
Yeah, sequoias are good, but it takes a lifetime.
These ones are gonna get packed in and they're gonna like it

We're prioritizing lettuces, and we salvage our store-bought green onion roots to replant, got 6 or so right now that'll go in.
Yeah, I don't intend on seeing those trees to maturity, that's not the point. If I wanna see the mature ones I'll take a road trip out to CA.