SPLaddict90, welcome to Audioholics.
My current build is going to be 2 tower speakers that are an old 3 way cabinet with a 12 inch woofer 5-1/4 mid and two spots for tweeters, I was planning on using parts express for the drivers looking into GRS and Dayton audio. the woofers are going to be cut at 80hz as I will be using two 15 inch subwoofer lpf at 80hz
Others (above) have already commented about your general plans. I agree with them, especially about the complexity of designing a crossover network for a 3-way speaker.
It might be worth the effort if you walk us through your thinking as you matched the 12" woofer to the cabinet you now have. Maybe you did it right and have nothing to worry about. And maybe not. I don't know how the car SPL guys design woofer boxes.
Once you're sure you have the cabinet right, you can begin to search for suitable mid range and tweeters. Pay close attention to the high frequency range for all your drivers. At what frequency does break up begin? Obviously, you want to avoid that. At what frequency do the woofer and mid range drivers loose off-axis loudness? When a driver's 45° off-axis performance drops 3 dB or more below the on-axis performance, the driver is said to begin beaming. This should be well below the driver's break up frequency. This is the frequency where you should consider making a crossover point. This is key to making a speaker have broad dispersion, and key to creating the impression of a 3 dimensional image of the musicians sitting in your room, not inside the speaker cabinet.
One last important point. Crossovers are best designed only after you have the drivers and measure their response vs. frequency AND impedance vs. frequency when mounted in their cabinet. Their impedance will vary across the frequency range. It is not a constant value. The crossover design software applications will take that measured data into account when coming up with a crossover. There are online calculators available, but most or all don't take variable impedance into the equation. They assume a constant impedance value, such as 8 or 4 ohms. Don't waste your time with them.
Your original post had several questions. You deserve some brief answers.
-what are you using for cross overs.
If you're asking about off-the-shelf vs. custom made crossovers, the answer is easy. Custom made is the only way to go.
You also mentioned a goal of 24 dB/octave crossover slopes. Learn (Google is your friend) about Linkwitz-Riley 4th order crossovers. LR4 crossovers will give the best chance of a flat frequency response (no dips, no peaks) across the crossover frequency range ±1 octave.
- are you using 3 way cross overs or individual hp filters,
Not sure what you're asking here. You should design individual high and low pass filters for each driver.
- how are you wiring the 3/4 speakers to get an 8-6 ohm load.
You mentioned one woofer, one mid range, and two tweeters, correct? Make your life easier, use only one tweeter. You gain little performance and lots of problems if you use two tweeters.
With 3 drivers, a woofer, mid range, and tweeter, questions of parallel or series wired drivers disappear.
- do you load ports off the wall?
Try to keep ports away from walls. In practice, this means keep a port at least as far away from a wall as the port diameter.
- do you want driver and port on same plane,
In my opinion, it works a bit better to have a port on the rear of the cabinet. A port on the front can work, but if it makes port noise (because the port diameter is too small), you'll notice it more if the port is on the front.