After you get boots that are just right for your feet, your stance, and your skiing style and ability, then get skis.
Buy used skis. After asking around a lot among good skiers, decide what type of skis you want. I'm in a big minority here...I strongly prefer a narrow waisted ski for packed snow. A ski with no more than about 72mm underfoot and 12 or 13 meter sidecut is so much fun on packed snow!...and because you bought used skis and bindings, you have money left for some fatties for deep snow. Any good ski shop can test the release of the bindings for you, as well as set the correct release settings and tune the skis.
About ski length...complex subject with little good info. As skis are made longer, they are made stiffer, within a given line of skis. In the same ski model, a 170cm is stiffer than a 160 cm. Length makes more difference than just how much sticks out front and back. Different lines of skis are stiffer or softer in the same length. And there are no standards. You really need to try different skis to find out which works best for you. A ski that is too soft won't perform as you'll like. A ski that is too stiff will take you for a ride, and not a fun ride. For my size, weight, style, and ability, I generally like skis one size less than the max available in that line. My 170 cm carving skis, my 184 cm all-mountain skis, and my 173 cm deep powder skis are all just right for me, and all one size down from the max in their lines. Your rule of thumb might be different. And if everything else is OK for you, different makes and models of skis will feel different to different people. The ski that puts the biggest smile on my face might not be the one that makes your day. Buy used and keep hunting for skis that are just right for you.