How do you determine how much to spend on speakers

A really good 8 ohm speaker could dip down to 6-4 ohms. A good 4 ohm speaker can go down to 2-.2 ohms. If your amp doesn't "double down" when resistance is halved , you're losing music. See what your amp can do , and buy speakers appropriately . Or buy an amp that will handle anything you throw at it and pick up some Maggies.

"How do you determine how much to spend on speakers "
More than you want too :-)

Based on my experience, I would definitely start the development of a system with the speakers. It is the speaker that mostly characterizes the sonic signature of your system. That is, electronics can change how well a speaker sounds, but they don't change the speakers' basic sonic signature. So, i would first make sure that I get a speaker that has a sonic signature I like. I would then try to optimize the electronics based on the speaker I've chosen. I don't think power cables make a huge difference. Interconnects and speaker cables, on the other hand, can make an enormous difference. The above probably suggests that the speaker is the hub of the system, something that you don't want to change that frequently because the rest of the system needs to be optimized on the speaker. For this reason, I would over-invest on it. How much depends on the size of your room. Smaller rooms afford you a smaller investment. I just bought a pair of reference 3a Decapo i for my smaller room...I invested $1200, and I believe it's hard to find much better speakers for a very small environment. Of course medium and large rooms require more expensive equipment...but even here, you can reach pretty good results with a $3K investment. If you like the midrange, for instance, Piquet modified ESL 57 is very close to the best...and they cost $3K.

My logic would be,A SPEAKERS and B AMP are the most important starting point.The rest in time.

Good Luck and have fun!

If I were you I would look at a Madisound Kit or similar if you are DIY inclined as this will save a heap. Zaph Audio/ scanspeak collaboration with Madisound the ZRT is a good bet. I would look at amplifiers next ME, Pass Labs, Accuphase, ARC, VTL second hand are sometimes a bargain. I would run a decent pro PC sound card with XLR out. I use an entry level ASI5111 that EATS most CD players up to $5000. Your computer and its music library are your source. Just thinking aloud you could run a SERIOUS amp with a passive volume control if it has XLR input and out. That is what I run on my PC only I run XLR to RCA out to a flea powered hotted Rogers Cadet III [8w/rms]into ProAc super Tablette with twin 8in bass bins a side run with a custom class A Amp
Loud enough for computer near field monitoring but not a lounge room but I can use the Tannoys for that. $5000 could build you a Killer system as you only need 3-4 components assuming you have a computer. Hope this helps