Ask Mr. Smarty Plants

The most important factor in establishing a meadow garden is good contact of the plant seeds with the mineral soil.  The seeds need this to have the maximum access to soil moisture during germination.  If mulch of any sort is thick on the ground surface some of the seeds will be trapped in the mulch fibers and not get the moisture they need.  So you would be wise to refrain from spreading any kind of mulch until after sowing your seeds.  However, after the seeds are sown, spreading a light application of mulch will help retain the moisture needed for germination. The mulch layer should not be so thick as to prevent light from penetrating to the level of the seeds, some of which need light for germination.

Freshly shredded cedar retains some of the soluble metabolites, such as sugars and amino acids, that were its nutrients when living.  When this metabolite-rich woody material begins to decompose, bacteria and fungi colonize it and can draw nitrogen from the soil, depleting the levels needed by your seedlings to thrive. Generally, this is only a problem when the products are tilled into the soil. For this reason, avoid using cedar chips where they might be incorporated into the soil layers, and save it for plantings where it can remain on the soil surface. After a couple of fall rains most of the soluble metabolites will be leached from the mulch and it will be safer to spread over the planted areas.

This article from the Lady Bird Johnson Wildflower Center web site gives more information on mulching.  And tips on wildflower planting can be found here. October is, as you plan, an excellent time to plant seeds, anticipating fall rains.