Lot of words here, let's break it down.
Building your own rigging, i.e., cutting the wire and installing the fittings can be a DIY job with expensive fittings or it can be done by a rigging shop for about the same money with swaged fittings. Swaging is not a DIY job.
If the mast is down, it is very easy to install the wires. Installing wires with the mast up is not a job for an inexperienced DIYer.
Tuning a rig is a skill that every sailor should learn, it is not a difficult task, a bit fiddly and time consuming, but not difficult. Depending on the rig your boat has, a more traditional rig or a B&R Rig, will dictate how much of a challenge tuning will be. A well tuned rig makes a world of difference in boat performance and reduces the chance the rig will come down.
Not all rigging wire is the same. There large variations in quality. Some of the best wire is coming from S Korea. Chinese wire quality, I'm told, is inconsistent.
Shopping cross border these days is a bit unpredictable given all the tariff talk. If you are traveling back to the US periodically,
Rigging Only is good rigging shop to use. If the mast is down, take the existing shrouds and send them to Rigging Only and have them duplicated. Most rigging shops will duplicate rigging and it is more accurate than taking measurements.