It's hard to say anything about your project from what you've provided here. Is this going to use a trunnion, or have a pivoting/tilting spindle? It's easy to specify all the things you want it to do; making it actually do them is harder.
1. A small machine like this doesn't need massive motors or screws; the structure needs mass, though.
2. I'm not sure what you mean by "proper". Welded steel holds together better than bolted, but the process introduces distortions that have to be dealt with. Fortunately small weldments are easier to heat-treat and grind than large ones.
3. Home switches make it easier to establish and re-establish position if the process is disrupted or a part is replaced in a fixture, but they aren't absolutely essential to the function of a servo motor.