For the back issue, start with lower weight or build up your "core" muscles better first before doing any other strength training. I am not a trainer, though!

Connective tissue = tendons, fascia, muscles themselves When working with machines like at many gyms, the movement is really isolated. Free weights are better since they kind of force your muscles into different directions. Kettlebells are a bit better in that regard and are more versatile and easier to use sporadically like in a home office environment.