speaker parameters

"As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. "

Click on Thiele-Small in the left column for more.  As far as determining what size enclosure, please read the sticky on using WinISD.  As far as measuring your own T/S parameters, this is not something for the average person to consider.  Why do you feel you need to measure them yourself?

Not average numbers.  To make an average, they would have to randomly select several woofers from the assembly line, test them, and average the results.  They don't do this.  The specs are obtained by testing one model woofer.  First runs are tested to match the model, and once confirmed is then mass produced.  The quality control on the Asian assembly lines nowadays is state-of-the-art and quite impressive.  The engineering of the model itself, not so much deviances in the manufacturing, is of utmost importance.

Quite frankly, if you are using a quality-engineered woofer the published specs will be close enough for the purpose of building an enclosure.  If the speaker maker's integrity is suspect, you shouldn't be using their products in the first place.  Right?  What you should spend your time on is mastering software that will help you in the box design process.  Now, if you have already mastered that important part of the equation and you have some money burning a hole through your pocket, look up "woofer tester 2" at Parts Express.com