Hi. You've got it correct. We generally scale up the motor to a maximum of a NEMA34-4 stack to get a peak force of 150 lbs linear. Keeping it direct driven preserves our near-zero backlash.
For use of smaller motors, a gear head is required, which as you say, adds some backlash, but not an appreciable amount of "springiness".
Our standard belting for ServoBelt is T5mm pitch, 32mm wide, so our recommended minimum pulley size is 15 teeth, for a linear travel of 75mm per motor rev.
Gearheads are readily available with 6 arc-min backlash, which at our pinion size translates into only .0008" on the linear. Not too shabby. You can get up to 10:1 in a single pass planetary to get that low backlash. Higher ratios/muliple passes (usually) makes for higher backlash. If you design your own, then smaller belt pitch is allowable, which on a 3mm HTD or T series can get you a smaller pinion.
Hope this helps!