Re: How long should the rope be?
Rope length is a matter of preference, but most would find 75 ft is too long if we're talking about wakeboarding. I know of very few wakeboarders who use anything longer than 70 ft...and they are the absolute best I know. Most use 55 or 60-ish. Keep in mind that you are yet another 6 to 10 feet longer for your particular setup...because you're attaching to the rear of the boat, while most wakeboarders are attaching close to the center of the boat where their tower hookup point is. So for wakeboarding on YOUR boat, you're effectively using the equivalent of an 81 to 85 foot rope...definitely too long.
Rope length depends exclusively on where your wake is shaped the best for whatever tricks you're trying to do. Beginners who are first learning to do wake-to-wake jumps and such will use a shorter rope (45 to 50 feet maybe??), simply because the wakes are closer together when you get closer to the boat (and often bigger)...both of which makes it easier to clear the 2nd wake. But this totally depends on the boat.
Then as people get better and more advanced, they'll generally gravitate to a longer rope because it will allow room to swing wider and build more speed (energy) to be able to jump longer and higher...and again basic geometry says that a longer rope will allow more room to jump higher as well. But that's getting prorbably more advanced than you are at this time, especially behind a bass boat. Even for those pros running faster boat speeds and running longer ropes, their ultimate length is limited by where their particular boat's wake is shaped the best. If you are riding back so far the wake has crested, then there's not much wake there to play with...and that's boring. So shorten it up and get into the sweet spot for your wake.
I believe most wakeboarding ropes people purchase are between 55 and 65 feet long. Better ones come in multiple sections so you can adjust them for your preference.
Most waterski ropes are purchased at 75 ft long, and again the better ones come in 8 sections that can be easily removed too allow multiple different lengths (this feature is primarily utilized for competition slalom skiing...but also often for just fine-tuning rope length for individual preference when recreational skiing)
The fact that yours is 75 feet tells me you likely have a waterski rope. If you are wakeboarding with a waterski rope you're adding some degree of difficulty...as waterski ropes are designed to stretch and have small handles, while wakeboard ropes are specifically designed to NOT stretch and have larger/easier to grab handles. If this is the case, shortening the waterski rope will also remove some of the inherent stretch...which might offer you secondary help in addition to the length change.
You can feel free to experiment until you find your happy place for your preference and boat. There's definitely no fixed answer to rope length. But for your setup I'd suggest as a random starting point knocking off about 20 feet. Don't cut it though...just do it with a knot so you can change your mind later and go longer or shorter from there if you choose to.
Keep in mind that as a general rule, if your rope is going slack at any time, on any length of rope, on skis or on a wakebord, this is simply an indicator of rider error and bad technique...and has nothing to do with the length of the rope. So if you shorten the rope and ride with the same technique, it will still go slack and will still drag...even with a pylon or even a tower.