Theme: Twenty Eleven. How to get the showcase running?

I’d like to get my new blog running soon but still have to be patient with all the technical matters blocking me.
I have chosen my main page to be the showcase template. I can only guess that I need Ephemera to start anything, that I also need to state the status of posts to appear in the showcase, but controlling fetured images and the look of the showcase lacks in tutorials that are clear enough.
Another thing that irritates me is no sidebar with individual posts, and at least an opotion for such on the main page. Of course I understand that much is possible but as for now I dread touching code modifications and extensive working with HTML, PHP or CSS, maybe in the future…
One question aside: I think it’s wiser to insert photos to my blog repository already made ‘lighter’, downsized than cropping or ‘thumbnailing’ them while inside WP – what do you think ?
The blog I’m asking for advice is still unfinished here:
https://cudownagdynia.pl/