can i play both guitar and midi keyboards at the same time?

Did you add an audio channel strip and assign the input to the Alesis Core 1?

I the example below I selected file>new, then a guitar amp template concert. Next, I went to layout and reduced the size of the screen controls to make room for a keyboard,, then selected a keyboard from the screen controls palette and dragged it to the layout.

Not sure what you mean. Do you mean keyboard and amp on the same patch? Of course. Create as many software instrument channel strips, external instrument channel strips, and audio channel strips as you want within the same patch.

Create a software instrument channel strip. Click on the right side of the input box to open the menu. Select Playback. To load an audio file click on the cog wheel to to the right of the file box. Select open file. For more complete explanation, select help>MainStage help. Then type in Playback plug-in in the search bar when the window opens.