You should be safe going as you are.
In my mind the “minimum safe zone” (at 5 node attempts instead of 8) is 30/100 - at that rate you can buy 2 refreshes (15 total attempts) for an average of 5 shards per day.
Week notice plus week of event gives you 14 days, so (14 x 5 = 70) is enough to complete the farm (and as others have stated, you can always pick up a crystal shipment or two if you are running below average on your farm. (And the 3rd and higher refreshes average out to higher crystal cost per shard than shipments anyways - on that note, don’t expect the cheaper cost you see with Nute and Dooku when the old republic toons come back around... the older legacy characters are 50 crystals per shard, newer characters are 80 crystals per shard in both daily and weekly shipments)