Hi Nemo
You should be OK with snow as they are really good at keeping the roads clear even if there is masses on teh hills and mountains.
Your route is OK but you could do that in a couple of days easily and there are plenty of really great roads just north which you shouldn't miss.
My own route would be head to Lake Tahoe and north to Chester which is just south of Lassen. There will be plenty of snow up there but the road should be good and believe me, it will be worth your while riding up into Lassen Volcanic Park as the road is superb and the views stunning. I'd then head East on hwy 36 towards the coast and the road is one of the best in the area. I'd then head south on via 101 and pick up the Avenue of the Giants which winds it's way through the Giant Redwood Forest. Turn right on Highway 1 and follow the coast and then pick up Hwy 128 to healdsburg and south to Santa Rosa. You can easily do this in 3 days if you are travelling on your own.
Alternatively, when you have been up to Lassen, you can come back south and take the superb Highway 70 through Feather Canyon. It's where the huge fires were last year but the road is delicious. Work your way over to ClearLake and then down to Calistoga. There is an epic back road which drops into the East side of Santa Rosa.
If you need any more help let me know.
Highway 70
<a href="https://chrisbiltcliffe.smugmug.com/California-2018/i-FKNP37x/A"><img src="https://photos.smugmug.com/California-2018/i-FKNP37x/0/059818aa/X2/2018-08-11%2008.48.25-X2.jpg" alt=""></a>
Bit murky up in Lassen due to fire smoke.
<a href="https://chrisbiltcliffe.smugmug.com/California-2018/i-8v5vD5T/A"><img src="https://photos.smugmug.com/California-2018/i-8v5vD5T/0/9d723e7e/X2/2018-08-10%2015.34.08-X2.jpg" alt=""></a>
Hwy 36
<a href="https://chrisbiltcliffe.smugmug.com/California-2018/i-rRd3Ndc/A"><img src="https://photos.smugmug.com/California-2018/i-rRd3Ndc/0/077976d8/X2/2018-08-10%2011.19.10-X2.jpg" alt=""></a>
Avenue of the Giants
<a href="https://chrisbiltcliffe.smugmug.com/California-2018/i-7sQBbZG/A"><img src="https://photos.smugmug.com/California-2018/i-7sQBbZG/0/61673cbe/X2/2018-08-09%2016.54.15-X2.jpg" alt=""></a>