The polls seem to decide quite a bit of the series, sans plot. Unfortunately, not all of them were broadcast well (at least, in English or otherwise easily found). As you mentioned, characters' hairstyles, costumes, and appearance were voted upon. I was unable to find these specific polls and their results. In particular, it does not appear that the actual poll pages are available anymore.
In addition to the character attributes, though, names of the group and the mini units were decided through polls, and there are frequent (and still ongoing) popularity polls. Some polls are used to determine character order in media such as music videos.
Dengeki G's magazine is the medium through which (most of) the polls are hosted. They, and their results, were printed in the various issues of the magazine, and conducted through their mobile site.
(Note: All magazines are published two months in the future. Here, I've used the actual month of publication, rather than the "issue date".)
The first through fourth popularity polls ran as follows:
- First popularity poll: Announced July 2010, ran from 15th-31st August.
- Second popularity poll: Announced December 2010 (could not find poll run dates).
- Third popularity poll: Announced July 2011, ran from 24th August to sometime in September.
- Fourth popularity poll: Announced January 2012, ran from 15th February to 10th March. The results (#1 Kotori Minami, #2 Niko Yazawa, #3 Maki Nishikino) were published shortly after.
The naming polls were early in the publications, following the first popularity vote:
- First idol group name vote: Ran from September to October 2010. After its success, five of the best names were chosen to be voted upon again.
- Second idol group name vote: Ran from 31st October 2010 until January. The winning name, "μ's" (muse), is announced.
- Three Units vote: Announced January 2011 (could not find poll run dates). The running unit names (Printemps, BiBi, and Lily White) were announced in February.
The popularity votes (or "general elections") were polls done for all the heroines of the show and were done by mobile phone site via Dengeki G's mobile site. I could not find the issue date for the 5th popularity vote, but it is ongoing at Love Live!'s official website, and will decide the central character of the 6th single music video.
Here is small publication of one of the results:
As for the rest of the polls' results, most of them can be found on the Japanese Wikipedia for μ's
and Aquors (screenshot here; they do not appear to be readily available anywhere in English).