STP and clients

Hello folks at networking, So far, thank you everybody who has answered previous questions and have helped. As you can guess, this one is regarding stp.

Now, 1. between two networks having two root bridge, would you keep STP running at the point of intersection or just do no spanning-tree ?

1. Apart from using STP, how you you automatically maintain redundancy between three or more interconnected switches?

2. What kind of incompatibility have you seen with cisco and other devices and their STP?

3. Is STP very important? Yes, yes it is.

4. If STP isn't used (no spanning-tree)at an intersection point between two switches of two networks, how would root or loop guard work? Or do they work regardless?

The reason I ask is because we peer with a lot of people, some directly to routers and some to switches and we find that peering with routers are the best but that is usually 1 in 10. A different switch means a different network and different kind of problem. Do you use any standard set of commands that go on every port? i.e root guard, keepalive, Mac access group, storm control?

Thanks, Niamul