Hello sir. I have 5 years of game programming experience and more than 2 working on Unity. I'm also a software engineer so I have some knowledge on network hardware. My suggestion is to make it in Unity. I don't even need any kind of plugin to make it possible: the ui would be done using Unity's own ui system, the available items will be stored on a DB accessed by a php server, the unity app will connect directly to the php server (I'm using this functionality in my current project). About the assets, I can buy them or just contract a 3d modeller friend (if there are not so many items, as this is expensive). If you're interested in my offer please contact me, the budget depends on how many items there will be to set.