Yes, you'll still encounter throttling even with 10DLC trust, it will just be less. If I remember correctly 10DLC is supposed to have a send rate of 15 text message segments per a second, although you can get that bumped up after vetting. But for example if you try to send 250K SMS at 10:05 am EST, those messages will be queued up and will be received by clients at varying times. This is something you'll want to monitor. If I remember correctly Twilio (and presumably other vendors) will show the actual sent time, so you'll be able to compare when you triggered a send with the actual send date. Unfortunately I don't think you'll see when clients actually receive the SMS unless you've got a personal phone number on your send list that you use to monitor. There are also daily send limits, which again can be increased after vetting. From a software engineering perspective SMS sending is really a series of queues. Twilio has its own queue per a number and a queue per a carrier. Each carrier maintains their own sending queues. As such, you'll want to monitor SMS sending the same way you'd monitor a queue ie by measuring throughput, and number of items in the queue.
Oh and I forgot to mention that if your SMS includes emojis, they get converted to MMS, which typically are more expensive. The companies I worked at, did tests and found that emojis didn't really impact response rates, although its worth testing your specific use-case.
With the double opt in, you probably don't need a blacklist, although you may want one for customers that reply with expletives, etc (assuming you're supporting 2-way).