Lavender should do great in the Willamette Valley.

I've had bad luck with lavender from seeds - it's not exactly the stongest germinator. I think my problem is that they apparently need strong light to germinate, and I'm not set up for that and the weather in Seattle doesn't really cooperate! I have gotten some to germinate, but the seedlings are slow growing and I eventually lose patience.

I would recommend that you buy small plants, if your budget allows. Little three inch pots are easy to come by and are cheap here in Seattle, and they grow up to gallon size in one year.

I'm having some success now with layering my older shrubs. I mound up soil on lower branches in the spring so that they are under the soil with tips peeking out, and then cut the rooted branches in the fall for a new plant. If budget is a problem, you might want to invest in a couple of big plants, and propagate them like this to get more.

My experience with starting Munstead from seed is that it is highly variable in size and structure. It does not come completely true from seed. I you are envisioning a line of Munstead along your pathway you may be disappointed with the irregular shapes you get. I've been told that none of the named cultivars come true from seed and if you want uniformity you must either buy plants or start cuttings. Very easy from cuttings. jwww

I have had some success starting seeds by the winter sowing method. (spanish and hidcote) Just transplanted about 6 or 7 plants from their one gallon containers.
Check out the winter sowing forum.
Duane