Simple. How big are the files? If you have an AVI file you want to add that is 13MB in size. Then the game will be 13MB in file size bigger. Scripâ€™s alone don't boost the file size THAT much, as its pretty much all text that is being read. It's the sound files, graphics and such that boost file sizes. Best way to measure the file size of the game is to check the file size of the files you are using.
If you use windows. Right clicking the project folder and going to Properties gives you the size.
As are as the files go. Anything that is inside your project's folder will be added to the games file size. So your question about deleting the default. Those files technically are not in your project, but running off the RTP installed somewhere else on your system. If you sent a game that used the RTP graphics to someone who don't have the rtp, then they can't play it.
If you look in the graphics of the project, anything with a BLUE icon is from the RTP. Anything in RED is in your project folder.
AVI/Voice acting sounds will badly boost the games file size. MP3'S and sound effects will as well.
It is a wise idea when you start a project to make it RTP free. I explain how to do such herehttps://taiine.wordpress.com/2011/02/14/free-of-rtp/
Also recommend reading about 'resource dumping' that is also posted there, that can also help cut back on bloated file size's by limiting the chances of files being added to your project that may end up not being used. https://taiine.wordpress.com/2011/02/14/sta...t-resorce-dump/