"BUT, I have questions:
1. Did Mormons, at one time, practice polygamy?"
There was a time where about 5% of Mormons practiced polygamy.
"2. Was it part of their religious tenets that they do so? "
It was part of their religion that they do so ONLY if specificly and individually called to do so by officers of the Church with the authority to extend such a calling on God's behalf.
THE DOCTRINE AND COVENANTS
SECTION 132
3 Therefore, prepare thy heart to receive and obey the instructions which I am about to give unto you; for all those who have this law revealed unto them must obey the same.
4 For behold, I reveal unto you a new and an everlasting covenant; and if ye abide not that covenant, then are ye damned; for no one can reject this covenant and be permitted to enter into my glory.
I report: you decide.
"3. Was one of the conditions of statehood a disavowal of polygamy by the CLDS? "
That makes no difference either way. It was the will of God that determined the course of the Church. The president of the Church clearly stated his intention to follow God's will even if it would bring far worse consquences than a mere witholding of statehood.
(You'll note the question was not answered.)
Yes, the United States would NOT have allowed UTAH to enter the Union, if the official 'state' church continued polygamy. You may find out the data by searching the web: I do not have it archived on my computer.