Once again I seek the advice from this much appreciated group of experts.

I fully expect this request to be very fundamental to most of you, so be kind I’m still learning.
My question; should I buy wheel spacers? What is to be gained? Are there any risks?
If your advice is to do so, how do I know the size? I see H&R has sizes from 4mm up.
My car: 1997 Porsche 911 (993) Daily driver only!
What I’ve done so far to the suspension.
1. Lowered with H&R sport springs, using Bilstein HD struts.
2. HRE 597R wheels. 18” x 10” rears, 18 x 8.5” front.
3. Rennline strut brace in trunk.
It seems that every time I open a catalog I see things I think I can’t live without. Am I just obsessing?
What would be your advice for additional parts I should consider?
Thanks so much for your time I greatly appreciate it.
James