Cheers! Yeah, I'm all over this. I'll definitely reach out.

I first got into Permaculture from reading my parents' copy of the Next
Whole Earth Catalog ~25~30 years ago. (Yeah, I'm a California cliche. lol)

Right now I'm living in a small townhouse in San Francisco with a tiny
yard. Somehow the covid virus pushed me to do what I can in the space
available. I got some chicks and we're raising them and I've been
growing things in large containers.

I can't really grow a lot of vegetables, we're out by the ocean so we
don't get the warm climate typical of CA and it's the wrong season for annuals anyway.
It was foggy 50F this morning. So I've been concentrating on building rich soil (for when I eventually
get access to more land.)

I take wood chips that have been amended with chicken manure and feathers
and layer it with Kellogg's GROMULCH[1], about four or five layers, water it
well, then broadcast a dense seed mix (different mixes in different bins,
whatever I have on hand at the time.) I call it "layer cake".

The GROMULCH mycelium rapidly pervades the wood and converts it to an
almost chalky consistency. (The earth "akin to the vegetative" of the
hugelculture quote.[2]) Part of the idea here is to see how well various
plants' roots integrate with the mycelium. Another aspect is that the
seedlings are so dense that their roots will form a mat or fiberous layer
over the whole surface. The leaves will cover the soil quickly,
protecting it and creating a moist micro-climate.

Before long the bin will be all soil (instead of half wood chips and half
soil) and it will be enriched by the growth of the fungus and plants.

At that point, I put the bin in the chicken run and let them eat the
plants, then dump it out and cover it with more wood chips and let the
chickens kick and scratch it out. I'll store it there and rake it up for
building planting beds in the Spring. Eventually, I can use the material
itself to make layer cake instead of buying more GROMULCH from the store.

In one bin I added some starting-to-rot lettuce and some woody growth
trimmed off a hedge, in another it's just wood chips and GROMULCH. In a
third bin I added some nightcrawlers...

Meanwhile, I'm starting perennials like dwarf tamarillo and alpine
strawberries, again for when I have access to more land.

Enough about me.

In re: your project, first, congratulations! I think you've identified
two key pieces of the puzzle: a plant database and a specialized online
marketplace. (The garden log and planner is also awesome, just I
personally don't see it as as big of a barrier as the other two.) I
think we also need a marketplace for land (Airbnb for small plots of
garden/farm, eh? Hosh mentioned https://sharedearth.com but I didn't get
any response from the site when I tried it. https://news.ycombinator.com/item?id=23887329
Hosh if you read this, sorry for not contacting you yet, I fully intend to...)

There are a few existing plant databases, mostly not as useful as they
could be, my advice there is to focus on standards and open data, don't
try to reinvent a wheel, rather engage and cooperate with the folks who
are already ahead of you.

Same thing with the specialized marketplace: there are e.g. online/digital
Farmer's Market systems and sites, but again, they don't seem as useful
to me as they might be. I'm thinking Craigslist+Etsy for handmade food
and food products, combined with scheduling and bidding features (e.g. I
am a chef and I want to plan out meals for my restaurant, the site should
help me pre-order ingredients. Or I am a grower and I want to pre-sell
my crops before I even sprout them... Eh?)

[1] https://www.kellogggarden.com/products/kellogg/gromulch-2-in...
They don't mention it on that apge but to me the big advantage of GROMULCH is the rich and active mycelium culture.

[2] "Then the earth itself will have the tendency to come inwardly alive
and become akin to the vegetative." ~ Herrman Andrä, 1962
http://pubs.cahnrs.wsu.edu/publications/pubs/fs283e/