You don't want the smallest file size here. Smallest file size means highest compression. And as you want to put this clip as source media in a premiere project I guess you'd even like to have no compression (-artifacts) to get highest quality and fast timeline scrubbing.
Don't care about 17MB files.
Alpha channel makes only sense with intermediate codecs (like ProRes). You need these in the editing process. When you're exporting a finished project you don't need it anymore. h.264 does not support it.
And I have a suggestion. Change the codec name "VoukoderR2" To "Voukoder“.Just like AE ,bro.