Welcome back to live sound! I'm an old codger, too.
The difference between 4 and 8 ohm cabinets, for me, comes down to this. If the cabinet has a single driver to cover any frequency and has a passive crossover, buy the 8 ohm version. Examples: any 2-way top with one tweeter and 1 woofer with a built-in passive crossover, or any single driver sub.
Any cabinet with two drivers covering the same frequency will be 4 ohm. Examples: dual 12" or 15" + tweeter top, or dual 15" or 18" sub.
When you get into the dual driver cabinets, provide you buy "good" ones, you have crossed over into a highly capable system. Examples: JBL SRX722 over SRX728, or EV QRx212 tops over QRx218 subs .
-Dennis