Please check the Limitations of KML/KMZ on Google Maps API:
Google Maps supports the following KML elements (that is, KML queries in the Search box and GGeoXml objects in the Maps API):
Placemarks
Icons
Folders
Descriptive HTML
Entity replacement via <BalloonStyle> and <text>
KMZ (compressed KML, including attached images)
Polylines and polygons
Styles for polylines and polygons, including color, fill, and opacity
Network links to import data dynamically
Ground overlays and screen overlays
This list does not apply to Google Earth's export to Google Maps, My Maps import, or My Maps export to Google Earth.
The KML parser generally silently ignores XML tags it does not understand.
Google Maps currently has specific limitations to the size and complexity of loaded KML files. Below is a summary of the current limits:
Note: these limits are temporary and are subject to change at any time.
Maximum fetched file size (raw KML, raw GeoRSS, or compressed KMZ) 3MB
Maximum uncompressed KML file size 10MB
Maximum number of Network Links 10
Maximum number of total document-wide features 1,000
Check the Directions API Terms of Service page which says:
Note: the Directions API may only be used in conjunction with displaying results on a Google map; using Directions data without displaying a map for which directions data was requested is prohibited
I believe that means you'll need to use the Google Maps API for your basemaps if you also wish to use their routing capability.
Best Answer
Google Static Maps API Usage Limits
If you think your website or application will generate high Static Maps image requests consistently in the long term, you should consider one of the following options:
Modify your application so that your usage is less than 25 000 Static Maps image requests per day.
Enroll for automated billing of excess image requests in the Google APIs Console. Additional image requests can be purchased at the rate currently listed in the FAQ.
Purchase a Google Maps API for Work license. You can buy Google Maps Enterprise here: https://www.google.com/a/signup/?enterprise_product=GOOGLE.MAPSENGINEPRO_STANDALONE&hl=en#0
https://developers.google.com/maps/documentation/staticmaps/#Limits