Opinion on 5 vs 7 channel and mixing brand speaker

Hi all. First of all, thanks for all previous advice. Finally got my amps in. MC205 and pair of MC601 and a used marantz av8801 processor. Need your option on the speakers set.

1. 7 vs 5 channel. Does it make lot of difference. I am currently having 5 channel (PSB image t tower, center and bookshelf) powered by MC205.

2. Mixing high end brand and entry level brand speakers for theatre? Any opinion on this?

I am debating if I want to make it 7 channel, the main speaker will be Wilson Sasha 2 and rest PSB. Or upgrade the 5 speakers and keep 5.1 while Wilson Sasha will be dedicated for stereo.

I enjoy both stereo and movie. But I spend just a little more time listening than watching.

Thanks for opinion.