My two cents-Your lack of practice time changes everything. If you have good multi-sport athletes on your roster who have decent instincts-I would utilize a press as a weapon to generate offensive opportunities. Wreak some havoc like Shaka did at VCU. Your defense becomes the catalyst for your offense. Rebounding fundamentals would be another focus. Can't score without the ball. Spacing and cutting to the hoop-Simple concepts that are effective at this level.
I forgot to add, our conference only allows press for the last two minutes of the fourth quarter, but we've tried a little bit of halfcourt trap too (with mixed results, and we'd need more practice to really get that right.
One thing we've really gotten better at is transitioning to offense after causing turnovers or grabbing defensive rebounds...unfortunately the transition offense is still a work in progress! The team can't make shots, but actually move very well without the ball during half-court possessions.
Long story short is you have an open roster and have little practice time. Oh yeah, it's also middle school. Are the kids safe? Are they learning about basketball? Do they support each other? Are they respectful to you, the officials, the opponent and the game? The more of those questions which get answered "yes", the better you are as a coach.
The answers to all questions are "yes", which explains why I guess I'm a really good coach for this age/level of basketball and thank you for saying that.
Being at a small school with no tryouts, it's really about the luck of the draw of the kids you've got. Over the last nearly three seasons, my guess my overall record is something like 3-21, but I actually have an undefeated season under my belt -- we had a kid who ended up playing D3 basketball, another kid who ended up a starting G for an LL CT public school and then a bunch of other kids that profile the kids I typically get: athletic kids, most of which are not from the USA, but work hard and are good teammates. If I wanted to, I could have won every game by 25, lol. About 97% of the parents are super cool too...there's one dad this season who isn't thrilled with our "lack of development", but I'm at an age where I can respectfully shoo off that bad juju.
A lot of my practices have focuses of "non-negotiables" that I might notice in a game that has nothing to do with skill. For example, on Thursday, we were completely out-rebounded, so basically I'm going to split the roster into three groups (three hoops available for practice) and have one kid practice shooting jumpers for 2 minutes each while the remaining students fight for rebounds. Two points for every made basket, but then one point for every secured rebound, no matter which team gets it.