I may have talked with you via email already and here's some honest advice. It's going to be hard to find a kite that works really well for both. Land riding should be done mostly with a foil especially when starting out. Years ago, I used to be intrigued by foils for water and winter riding on snow, but most everyone who used to ride foils, has switched back to inflatables or stayed there. I've ridden some of the best Ozone and Flysurfer foils that cost over $2800 and really wanted to like these kites, but I much prefer high performance, high depower inflatables.
In my opinion, modern inflatables are much better in gusty winds, have more depower (generally), are more predictable while jumping, have better feel, are faster turning and if wave riding, it's not even a choice....foils can collapse and buckle and get lines messed up around the kite and it's then a swim in.
It's going to be hard finding a lot of info on landboarding (very few kite dealers carry boards) due to very little demand for it generally. I talk to a lot of people weekly about gear, lessons, etc. and have only had 2 people ask any questions about landboarding in 4 - 5 years.
If you want to do it, find a used board somewhere and you could use a inflatable on land if the land has smooth mowed grass. There are some videos of top lanboard riders using inflatables and these guys are doing some insane tricks, but they hardly crash their kites and / or are riding in really nice fields.
I hope this helps and let me know if I can answer any other questions.