Hi Russell,
You've already got a lot of great advice, I just thought I'd add my 2 cents. I started using BIAB for a one man band gig 10 years ago. For me personally, using a laptop instead mp3 player works best. As mentioned in other replies, you can't modify things on the fly like you can with a computer. What if you want to do an extra chorus or a singer wants to sit in and do "Bye Bye Blackbird in "A"? Until real drums and real tracks, you didn't need a real fast computer so I was using a dell latitude I bought of ebay for 200 bucks. The real tracks sound great but the do take some time to load. It may not seem like much time but on a live gig it feels like a long time. You sound like you have a pretty new computer. You might want to do a combination of things. Render some songs and use biab for others. You can play the rendered songs while loading your next tune from biab. The sound system depends on how big a place you are playing. Speakers are probably the most subjective thing in music. Some people swear by Mackie while some people think they suck. I would go out and listen to different groups and their setups to get some ideas. Ask groups about what they are using. I find most musicians to be very gracious when it comes to sharing info and experiences. As far as protecting you laptop from harm, that's no different than protecting you axe. In fact in the backing track situation it is your axe just like your guitar or keyboard. Good luck to you!

Dell Studio 16 Laptop i7 with 256 gig SSD
BIAB, Reaper, Encore, Sibelius
Roland SD-50