The main issue I see is that you'll need a secure, well-reinforced joint between your wooden keel's forward end and the upright (metal?) that holds your headtube (which will also need to be securely mounted to the upright). The forces on that area especialy under even minor bumps will be huge, and can cause catastrophic failure while riding. Depending on the materials used, it can be sudden and without warning.
I used welded steel to build the SB Cruiser from, and I still have a weak point in the design involving this issue, where the loading at the front edge of the cargo/seatbox has twice broken the keel. That specific failure mode probably won't happen on yours, depending on the size of your keel (like a 4"x4" post) and how you mount the seat to it, but the laoding on the headtube/downtube/keel mounting point will be very high in lateral and forward/reverse directions which will occur all the time while riding. Vertical loading will also happen, but that's easier to build for. The ability of the wood to twist in torsion will help with the lateral loading, but the forward/reverse loading could cause the whole front end to snap off at that point once enough damage to the joint occurs.
Adding triangulation from the headtube down to under your seat, as far back as is possible to do, will help, but the specific method chosen to connect the different materials will matter quite a bit.
Optionally, you can use a handbike attachment for a wheelchair (either already equipped with a motor, or not) as the front end of the trike. That would also solve you having to build the handbike cranks out of regular pedal bike cranks, as well as adapting that bike's bottom bracket (BB) frame / etc onto a fork's steerer.
Parts are easy to salvage from other old bikes from bulk trash piles, local bike shops or coops that keep scrapped bikes aorund for parts, thrift stores, freecycle / trashnothing / craigslist / etc. That's been my sources for almost every bike part I need for my builds. Most of them were free parts, others extremely cheap.
BTW, for the seat itself, given your drawing, I would recommend the StadiumChair (as I use on my rides) as it will save you construction work (even if you have to modify it for a more reclined position) and it is quite a comfy seat even for long rides. The company itself is responsive to customer inquiries as well. (there are clones of them, but they are not nearly as well made, and their steel is much heavier and cheaper and weaker; I have both types). They also make wide versions if you don't like regular seat widths.
If the "wings" on either side of your front wheel are footrests, you may need to build those onto the fork itself rather than the trike frame, so that they pivot with the wheel, or you may have to place them quite far apart to give the front wheel space to turn. If you only need to make very wide turns, it won't take much space, but if you ever have to make tight turns it could be a serious problem if they're too close to the wheel and mounted on the trike frame. But mounting them to the fork means they will move out from under your legs while turning, and the sharper the turn the worse the problem. Depending on the level of control, feeling, strength, and movement you have, it could be possible that unless they're strapped or clipped in, your feet could end up "sucked" under the trike after falling off the rests.
For the rear end, there are several ways to mount the wheels, depending on which wheels you want to use, and which motor drive system you prefer. There are trike kits designed to turn a regular bike into a trike which would make it pretty easy to build the whole rear around. That's how I built both Delta Tripper and the present SB Cruiser, and the Schwinn trike conversion
Amberwolf's Schwinn Trike Rebuild / Conversion to Heavy Cargo Hauler also has one though I'm not using it that way.
Or if you are building from scratch, you can use a differential (like peerless, or cheaper versions of the same type of thing such as were used on the ancient Schwinn trike I'm converting in that thread above). Then the chain can drive the diff, which then drives both wheels even when turning.
With a diff, you can either drive the diff from a mid-mounted motor (even a hubmotor mounted without a wheel) along with the pedal chain, or you can use hubmotors in the front and/or rear wheels. If you use them in the rear with a diff, you would either need to customize the hubmotors to mount to and work with a diff's live axle, or you would need to do something like I am doing on that Schwinn conversion, where a chain or belt from the outboard end of the diff axle drives a sprocket mounted to the motor casing (with or without a freewheel depending on what you want the system to do for you).
You may also want to look at my SB Cruiser thread for an example of a working delta trike design. You can easily leave off the cargo box on the back and leave it an open deck or even just open frame, but it's been working for me for about a decade so far.
The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier
There are many other possible trike designs as well; and many threads about them here on ES with discussions of CoG, wheelbase, width, height, steering considerations, wheel drive methods, etc., if you haven't already found them.
