Order of importance and budget percentages

Components first (seems you’ve got that covered), room next. 
Then…power conditioner for your source, power cord for the conditioner, power cord for the amp, speaker cables next. Interconnects, USB, ethernet. 
Get the best you can even if it is gradually one cable at a time. I’m not inclined to set budget limit of percentage of the component cost as I don’t adhere to any of these guidelines in my system. Get used from reputable sellers. 

So you already have passive speakers @systembuilder ?
The speaker cables are generally more important than ICs, expect maybe TT IC.

I would go 50 to 60% speakers, 30 - 35% on Pre/power/integrated/sources, that should leave about 15% at least for room treatment, and maybe 5% for cables and power conditioning. Don’t spend more than $10 on Ethernet. Uptone and other products are 100% snake oil. 

I’d spend $20k on speakers, $10k on amp/pre, $10k on source, $5k on cables, and $5k on a power conditioner for a $50k system.  Just a rough guideline, but adjust as necessary as overall system balance/synergy is absolutely key.  I left out room treatments, but they’re likely a necessity as well to get the most out of the system.  

@soix +1 

My breakdown is similar - budget and breakdown.   And I expect my system may evolve in the future; however, I expect my cables /power accessories are my forever cables.