Power Cord is a soft polyester, but it is still a polyester: it won't feel like a multifilament, and it keeps the firm, controlled response you're used to.
If you like what poly does for your game but wish it were livelier and more forgiving, this is the one to try. And if a full (non-hybrid ?) poly bed has been harsh on your arm, Power Cord's extra elasticity gives you a softer string bed without giving up the spin of a full poly setup.
Start at whatever tension ? has worked for you in other polyesters.
If hitting harder with more spin appeals to you, polyester is worth a try, and Power Cord is the easiest one to start with. Any move to polyester means a stiffer string bed; a softer poly like Power Cord keeps that jump small.
To keep it smaller still, start with a hybrid ?: Power Cord in the mains, a softer string such as Golden Set Synthetic Gut in the crosses. You'll get impressive spin from the hybrid alone. If it works and you're open to a little more firmness, go full Power Cord on the next restring for even more.
For tension ?, start on the lower side of your racquet's recommended range; polyester can go surprisingly low before control suffers.
Power Cord's extra elasticity may change your mind about polyester. It has the spin of the poly family with a noticeably softer, livelier feel, and many players who try it don't go back.
Two things to get right, though. Since stiffness is what put you off, don't play it as a full (non-hybrid ?) poly bed straight away, and don't string it as tight as the poly you found too stiff.
Pair Power Cord mains with a softer cross such as Golden Set Velvet or Synthetic Gut, and go a few pounds lower on tension ? than last time.
Start on the lower side of your racquet's recommended tension ? range. If it still feels stiff, drop a few pounds more on the next restring; polyester can go surprisingly low before control suffers.
Use whatever tension ? has worked for you with other polyesters, and adjust from there: lower for more power and comfort, higher for more control.
Go with 17. The thinner gauge ? gives you more feel and more spin, and if you rarely break strings the extra durability of 16 isn't worth what you'd give up.
It's a trade-off: 16 gauge ? lasts longest, 17 plays with more feel and spin. A good compromise is 16 gauge in the mains and 17 gauge in the crosses. That hybrid ? gives you close to 16-gauge durability with some of the 17-gauge feel.