Is there a magic formula for spending on components in a system

Not big into formulas, but I am big into what sounds good and works well together. 

Magic formula is simple.

Spend right up to your limit...or to all you can afford...and you'll be there.

yes, it is about 3% of your yearly gross income or $15,000 whichever is less. 

To me, speakers have the biggest impact and variation on sound.

So, about 1/2 on speakers, then work out the rest from there.

I had such a clever response nearly completed when I left the page and lost it all. Now I must to condense the wisdom. Prepare yourself.

If you had $10k to spend,
( I'd suggest seeking financing for an $10k. haha-joke).

I will preface my remarks with full disclosure that you are reading a recommendation by someone who is enjoying his 2nd double of  Jethro T. Boots Kentucky Whiskey. CVS $8.99. Really tastes about the same as the $80 Japanese whiskey I had last week.

As the acknowledged weakest link in audio is the speakers,
you start there. Spend 6-12 months investigating what you want.
Find what you like. Not what somebody else likes. $4k is the max
you spend here. Leaves $6k. I am pretty good at math.

Then you will know what type and how much power you need. 
Your two brands to choose from are: Pass Labs and Line Magnetic.
If your speakers require massive power then I will offer a 3rd choice
for amplification. Magtech by Sanders. 

You buy everything used. From the original owner. Under 1 year old.

For a source-Stream with your own computer. Hardwire ethernet to your DAC to your router. Buy a Preamp/Dac combo for $1k. $5k left.

Pay $700 for a lifetime subscription to Roon. $4,300 left.

Hire an electrician to install 2 dedicated runs to your HiFi.
The cost of this will vary. Include the ethernet line. I did 
it for $350 at my house. Likely you will spend $1k.
$3,300 left.

Cables.com.  Buy used interconnects. Buy Kimber cables. 
Budget $1k. $2,300 left.

Buy 6 each  2' x 4' absorbing panels. Cost $60 each if you buy
new or $30 each if you make them. If you have a hard surface floor
get an area rug. Deal with windows with drapes. Cost $500.
$1,800 remaining. 

If you have LPs, buy a used Rega TT and a Schiit audio Phono stage.
End of original $10k.

That's all folks!!