I'm wondering if it's legal to collect a physical deposit and then also require the above guarantee premium?

Just note that wholesalers typically acquire off market properties at a deep discounts because the property is often in distress (financial or physical) sometimes both.

Most of these look like they in 3X better physical shape than they did 10 years ago.

Its separated on all sides from growth: To the east, the railroad tracks and industrial area create a physical barrier, to the south, the BNSF tracks do the same, to the north is 290, and to the West is more tracks and industrial area.

It may not be tangible in the sense that you can hold physical BTC, but the code that surround BTC is irrefutable.

So prepare yourself for that mentally and physically. 

The Lessee of a property lease will most likely be required to have the leasehold interest subordinated to any debt placed on the property for physical improvements.The Ground lease should address subordination at its inception to avoid any complications that might arise if and when the Lessee decides to improve the property.

I’ve since developed physical access to the property, including 2 lots that are now buildable when there was originally no access to the property.

You can't cut corners, and you can't do it on the cheap and still be protected.If you rely on an entity or entities to protect you then you should not physically provide any service directly.

Are there any physical offices in Houston?