It will be challenging day. Start early as possible to avoid heat and crowds. Combination of inclines and wind on the 145 will wear you down by the time you reach intersection with 606. If you are coming back the same way, like I did, leave any extra bags, that you won't need up there, at the local restaurant. You will be thankful for this advice later. I reorganised my panniers and managed to leave 2 of them.
Yes there are many hills coming up but what's new, this is CR, My main problem were not the inclines but insane amount of traffic. Combined with very bad road conditions, it becomes dangerous and life threatening. Stay away from the shoulder, it's soft gravel and dust that will flip you in the ditch.
If it is not on your must-to-do list, I would skip it. Take the bus and enjoy the views. Remember, you have to ride back the same way out!
Between km 18-21 my phone overheated and shoot down, so be aware of that too.
Good Luck!