Hi Tj,
I don't think you need to go crazy about your tape storage. The Tape Project tapes are pretty well packed and as long as you store them upright in the temp you stated, and in a
played (rather than rewound) state, you should be fine. You should avoid having direct sunlight and the vents from your heating system from blowing directly on them. So, really, if it's ok for you lp's, it should be fine for most tapes.
Older tapes may require just a little more attention. If you have a number of old acetate tapes long term exposure to very low humidity can cause some problems. You mentioned installing an humidifier. I'm not sure if this is really necessary. If you use slip covers over your tape boxes with a seal (which doesn't have to be air tight), I think it negates the need for special equipment in all but the most adverse conditions. They also protect the boxes and isolate the tapes from each other in case one develops mold at some point (it's best to toss any tapes that develop this problem).
I buy my slip covers from a fellow on eBay. They're under $25 for a pack of 100 and are very nice.
http://cgi.ebay.com/100-Acid-Free-Reel-to-Reel-Reusable-Clear-Pro-Sleeves_W0QQitemZ300373375166QQcmdZViewItemQQptZMusic_Other_Formats?hash=item45efa5f8beSince they seal about 80% (just a WAG) they keep sudden changes in temp and humidity from reaching the tape and they give me a place to affix labels too.
About the only tapes that would benefit from a humidifier are ones that are already showing signs of "vinegar syndrome". These are easily found by the smell of vinegar and many times the inside of the box will have an outline of the reel "printed" on it by the acid that's been emitted by the tape. You can help slow this process by sealing 100% in a bag with fairly high humidity. I usually just use freezer bags and seal them in a steamy bathroom. This is totally unscientific of course and the added humidity can lead to mold if the spores are present. Out of the many acetates that I own, I've only bothered to do this with a couple.
Really important tapes that have loss of lubricant or vinegar syndrome should be sent to a real restoration/archivist for transfer and treatment.