FCP7 best export settings, format & codec suggestion

hello,

I write to the forum to ask you some questions on codecs, compression types
for small video i made using canon 600d and shot with built-in mic, 25fps, 1920x1080p

After i converted the MOV files to proress (choice listing proress only without i.e. LT) with mpegstreamclip, and moved the clips on timeline, set for proress codec, i made a 15min approx. video and want to export it in the Smallest possible filesize and in very good quality for Ytube first.

When exporting from FCP, i use QT conversion, Apple intermediate codec and export.
File is about 11GB in size, huge ! Then i convert to 720p with mpegstreamclip because i dont know
how to shrink it properly and i get a 500MB file using h264, AAC sound and fast start.

I am not sure if 11GB should be that big, but i have seen movies claiming sizes i.e.150MB and very crisp almost uncompressed quality for Ytube, and i wonder if you can help me pick up right choices to export a small file size for a start and also in full HD.

When i play my file, i have some dark areas, i.e. swarm of bees hanging on a tree branch, which i want details Not to get very compressed, as i see no bees, just artifacts, and i was wondering also if there is a way to tell FCP or mpstreamclip, not to compress specific frames on my video etc.

any help on the above will be appreciated
Thanks