1) The two "teaser" templates can be used to start off with when you're about to create an article. Either you search for a WordPress post to create an article out of or use one of the teaser templates.
2) What your'e describing regarding the text editor seems like a bug. I would guess that the cause of this bug is related to your installation of WordPress, some other plugin messing things up. If you can try to deactivate all plugins and see if it still behaves the same way. What browser are you using?
3) You can not toggle the font size by clicking on the up/down arrow keys, your meant to drag the slider with the mouse. You should however be able to focus on the input and type in the font size (I will look into that)
Question: Are you still using the page template called "Article list page"? You should change to any of the other templates and choose the article list in the meta box called "Arlima". There you will also find an input labeled "Width" where you put the width of your article column, this is used to calculate the the size of the images. How wide you should configure the list to be depends on your template.