Having a tight integration with your scale is an important component of your cannabis business process. For both harvesting and packaging connecting the scales directly to the software increases accuracy and efficiency. Larger scales on harvesting allows for faster entry for both large batch and individual plant harvest processes. Multiple smaller packaging scales can be connected for a continuous weight feed with reports for production volume.
Your cannabis business may be subject to rules imposed by general state regulations regarding weights and measures that are outside and independent of the cannabis regulations, such as one of these agencies.
Additionally, each of these departments have their own rules about calibration and what constitutes a "legal for trade" certification. There are many service providers who's sole offering is the integration, calibration and maintenance of scales, such as Alert Equipment Unlimited in Oregon. You do not need to find a cannabis specific service provider; agriculture and restaurant providers can help here.
These are generally going to be some large size scale that is capable of weighing up to 250 Kg (~550 US lb)-- sometimes even more. Depending on where you are located some laws may limit the amount of material you can process; use those factors when deciding on which hardware to purchase.
These types of scales will generally RS-232 to some input and capture the weight on demand (via button, or foot-switch) to transmit the value to the software. Other scales can be continuous data-stream; you just wait for a "stable" value to appear.
Use a standard bin for containing your harvest materials, always use the same type and tare your scales to these bins.
These are little tiny desktop types such as this Ohaus R31P30 but you need to be sure to pick one with high accuracy. Packaging small amounts of Kief, Rosin or Wax will require high accuracy (eg 1 mg) so you may need something like this Lab Scale.
Packaging requires lots of tedious entry into the system, so software integration is necessary for performance. And, if all the scales are configured with continuous scanning then your packaging cycle can be measured by frequency of movement from 0 to $PACKAGE_WEIGHT.
Multiple USBs to feed one computer (or even a Raspberry Pi!) and use a big USB hub like this 13 Port USB or this 20 Port USB or this 28 Port USB that looks kinda cool; or this 32 Port USB an absolute unit.
Get familiar with your government regulations on weights and measures. Find a weights-and measures service provider. Get a good scale and then plug that into your software.