Hi there, we’re looking to integrate with NetSuite and build it in house. We have lots of transactions that occur throughout the day with peaks as high as thousands within an hour, given we have order and fulfillments. What technology api should we consider? SOAP vs REST. My concern is outage, time-outs and reliabilities as some of my transactions can contain many lines

REST is easier. You other concerns aren't really issues - when you design interfaces you retry when endpoints are unavailable. As far as throughput is concerned - this depends on the number of suitecloud+ licenses that you have, and the limits are concurrency based, not N transactions per period of time. That is all explained in the documentation