A - Yes you can, but you might want to get some experience using the engine, even finish a smaller game before you start implementing such functions.
B - You can create your own save system using JSON and NW.js.
C - Are you talking about global variables? You can also pass data using objects' instance variables. Just look into the manual to set them up properly. https://www.scirra.com/manual/73/instance-variables and https://www.scirra.com/manual/83/variables
D - Yes, you can include event sheets into each other. Just right click on an empty space on your event sheet and select "Include event sheet".
E - I believe you are talking about the dictionary object: https://www.scirra.com/manual/140/dictionary
F - Unfortunately you can't. The only way for this to work is to make a plugin.
G - Depends on what game you want to make. Keep in mind that this is a 2D HTML5 game engine. You can make serious games with it, but it takes practice (just like with any other engine). It's more likely that you'll first run out of hardware resources before you bump into an engine limitation. But if you have specific questions about limitations I try my best to answer them (for ex.: Can you do 3D? No, only with the Q3D plugin.; Can you export native applications? No, you can only export into either HTML5 or using wrappers to get an application (for Windows with NW.js)).