How to measure weight?
Here is one way to avoid load cells, bridges and all that with something possibly easier. Since you have a way to mechanically support your hive (Which sounds huge! Mine are not near that heavy even when three boxes full). 

How about a simple balance and a water tank on the other arm? Pump water in or out to get balance. There are a lot of nice ways to measure depth of water in a container. You can also continuously fill till balanced then measure contents as it empties. A dump bucket as used in rain gauges could work for both in and out.

Compression of a spring with or without a lever is also good. Have you looked at the load cells that you hang something from?

Personally I like measuring ml of water to get grams - sealed of course or your bees will keep moving it into the hive :-)