I'd suggest using the XLRs from mixer to speakers. Firstly, they are a bit more robust than TRS. Secondly, it means you only have to cart around two types of leads: power cables and XLRs.
There's no difference electrically or in terms of sound quality. However, I lean towards XLR because they're a locking connector, much less likely to be knocked out by a staggering drunk. (Then again, the TRS is more likely to pull out rather than breaking the connector or knocking the speaker over!)
Yep, XLRs lock which can be bad or good depending. Some XLRs omit the latch. Snake heads often do to make disconnection quicker.
XLRs also don't short when you plug them in as 1/4" do. That's not a big issue at line level but for passive speakers Speakon is preferable because they lock and don't short.
In hundreds of live shows I never ran a stereo PA in my life. Every channel panned dead center. Do mono unless you have some extremely compelling reason to do otherwise.
Thanks for the cable suggestions everyone. Greatly appreciated. Looking forward to getting this first PA rolling. Not looking forward to being the drummer AND soundman.