Doing a custom build from scratch is complex, orders of magnitude tougher than a kit.
First off, you need impedance and frequency response sweeps of the drivers individually, with no crossover present. For this you need some basic equipment, I use this gear and a DIY turntable stand I built. For an amateur, this is enough to get you a good sounding result. The gated measurement process just lacks low frequency accuracy.
https://www.parts-express.com/Dayto...ter-Based-Audio-Component-Test-System-390-807
https://www.minidsp.com/products/acoustic-measurement/umik-1
For more details on this process, check out this thread:
https://www.audiosciencereview.com/...ents-spinoramas-with-rew-and-vituixcad.21860/
Before you go designing a crossover, first take a look at the impedance curve and waterfall plots. If you see a lot of stored energy, that indicates resonances which may require cabinet modifications to fix. You should also test the drivers outside the cabinet, to see if the resonances are not caused by the cabinet at all.
Once you have finalized measurements in a cabinet with no resonances, then use VituixCAD to design a crossover. An ideal speaker has an off-axis response which follows the same trend as the on-axis response. Narrow vs wide dispersion is a matter of preference/usage.
The Tannoy M3 is an example of a wide dispersion design due to the dome tweeter with no waveguide. Expect to see a sharp discontinuity between the off-axis response of the woofer and tweeter at the crossover point. This is due to the size of the woofer causing a narrowing radiation pattern before the tweeter takes over. Smaller drivers are less prone to this, hence the best speakers having a dedicated 2-4" mid-range driver, or even a full co-axial arrangement like the KEF R3.
When designing the crossover, start by looking at the distortion profile of your tweeter. You must crossover before high distortion appears, to avoid severely reduced power handling and audio quality. If the tweeter distortion is negligible, measure the on-axis frequency response at a higher volume, in 3dB increments until you find the distortion point.
Then add a simple 2nd order filter to both the woofer and tweeter at your chosen crossover point, and l-pad the tweeter so the overall volume is the same. First order filters are too shallow for 99% of drivers. You may need to implement 3rd or 4th order filters, in order to have proper phase alignment at the crossover region, meaning no peak or dip in the frequency response.
Once you have a basic crossover worked out, you may want to implement notch filters, adjust baffle step compensation, or create non-uniform filter slopes by adding resistors. When you finally have a version you are happy with, order the parts to build it. Go cheap on the capacitors and resistors, air core for the inductors if within budget. Iron core isn't horrible, but will add some distortion, particularly at high volume due to saturation.
