1. You are right, we will probably add a custom code box in the Customizer in the next update.
2. You should be able to change it in TG like any other block, using Decorations -> Background color. Notice that you need to do this over the main parent of the footer.
3. As you say, there is only 2 sections now. Do you think that a max of 4 columns would be enough? We do not want to give users a lot of freedom here, since some newbies can “destroy” a beauty design using a lot of widgets or wrong settings.
1. Have you tried the slideshow block? We are using it there. We plan to use the same method for future blocks integrated like plugins (ie Contact Form 7) or even for some default recommended plugins.