I have been through Johnstone Strait 10 times; 8 time while going around the island, twice last July on a trip Comox - Port Hardy - Comox.
As I try to miss Chatham Point, I usually avoid Seymour Narrows in favour of the Yucultas. Surge Narrow / Upper Rapids will take you past Chatham Point, but the stop at Octopus Islands is very nice.
Read either Dreamspeaker or Sailing Direction for the instructions to get through the Yucultas, it is not that bad, but can only be done once a day. Plan ahead.
Blind Channel is a good place to check conditions in Johnstone before venturing further, the marina has free wifi
From there follow Cordero Channel (if conditions are good) or go through Sunderland Channel via Whirlpool Rapids back into Johnstone.
I take Havannah Channel / Chatham Channel to Lagoon
Cove (funky marina) or Poots Lagoon
(well protected) or Cutter
Cove (open to the west). Avoid Port Harvey - way too much logging activity.
Then Baronette Passage
into Johnstone Strait again for a short hop to Telegraph Cove. Why stop there?
Check Sailing Directions for the average weather
conditions(or I could post it).
The winds seem to favour you on the way up. The way back wil be a beat.