@slobdiddy Looks like you've given this some research and thought. That's always a good investment. IMHO, you've made some good choices; so most of what I have to offer will be a "devil's advocate" type of response.
I do have just one concern - especially given the shipping delays you mentioned that presumably would delay a return, as well. Without a compelling reason to do so... I'd be reluctant to upgrade RAM capacity beyond what's officially supported - and I'd be reluctant to use non-Synology RAM. I don't see anything in your description of workload that screams out "memory upgrade". If you do proceed with the RAM as part of your initial "package", I'd suggest using the
1019+ with factory memory for a while before swapping out the memory cards. RAM upgrades are always tempting; and relatively inexpensive. But often not necessary.
The IronWolf M.2 cache drives should be fine. But they are almost certainly at least a 4x overkill in terms of capacity. But given your analysis of cost/GB, the 480GB is an easy choice.
IronWolf Pro is, IMHO, a very safe and logical choice. But you might also look at Exos before buying. Exos is more durable, longer MTBF, etc. And they are often less expensive than IronWolf Pro. HOWEVER, there are some noteworthy tradeoffs: Exos drives are heavier, consume more power, generate more heat, make more noise, and must spin 24/7 (no hibernation). Also, there's no data recovery option.
FWIW: We recently swapped out 24x older IrowWolf Pro 10TB for 18x Exos 16TB. They're in two NAS in an unused room that we now refer to as the "bamboo forest".
Not to second guess... But if you're looking at this purchase for the long haul, do be sure you've over estimated data growth through time, such that your data will not exceed about 80% of the array's actual capacity - lower is even better. Note that the "labeled" capacity of a hard drive is larger than the available capacity when installed. For instance a 16TB drive will have about 14.6TB usable capacity.
Well that's my two-cents-worth. I'm eager to hear your thoughts, as well as others.
Ron