I'll respond to your tax question first, since that's a shorter answer:
- Enable Sales Tax/VAT in the settings of each product that should charge tax;
- Go to Seller Admin > Cart Sales Tax & VAT Settings;
- Check "Tax buyers from state" and select California;
- Sales Tax/VAT Rate: enter your general tax rate for CA buyers;
- Advanced Sales Tax Settings: here you can enter a list of ZIP codes with the tax rates those ZIPs should be charged, overriding your general CA rate; you can specify partial ZIPs to cover a range, and more-specific ZIPs will override less-specific partial ZIPs -- e.g., if you entered the following:
921,8.5
9212,9.1
92123,9.6
...then ZIPs from 92100 thru 92199 would get an 8.5% tax, except for 92120 thru 92129 which would get 9.1% tax, except for 92123 which would get 9.6% tax.
Now, for your shipping, enable Shipping/Buyer's Address in the settings of each product that should calculate shipping charges and trigger collection of an address during checkout (the product's other Shipping Options settings won't matter in this case, so you can just disregard those).
Go to Seller Admin > Cart Shipping Settings and set up the following:
- Shipping Origin: select United States and enter your ZIP code;
- Shipping Destinations: if you will only ship to certain countries, select them in the list, or otherwise select nothing for Worldwide shipping;
- Leave all other settings blank or 0.00;
- Click Next to save settings and proceed to the Shipping Rules screen.
In the Existing Shipping Rules menu, select and Delete any Rules you may have saved there.
Set up your first shipping rule for domestic Priority shipping on 1 item:
- Shipping Rate Calculator: Flat;
- Shipping Amount: [Enter your A1 rate here];
- Shipping Method Description: Priority;
- Max. Items in Cart: 1
- Country: United States;
- Click Submit to save the Rule.
Next rule for domestic Express shipping on 1 item:
- Shipping Rate Calculator: Flat;
- Shipping Amount: [Enter your A2 rate here];
- Shipping Method Description: Express;
- Max. Items in Cart: 1
- Country: United States;
- Click Submit to save the Rule.
Domestic Priority shipping on 2-5 items:
- Shipping Rate Calculator: Flat;
- Shipping Amount: [Enter your B1 rate here];
- Shipping Method Description: Priority;
- Min. Items in Cart: 2;
- Max. Items in Cart: 5;
- Country: United States;
- Click Submit to save the Rule.
Domestic Express shipping on 2-5 items:
- Shipping Rate Calculator: Flat;
- Shipping Amount: [Enter your B2 rate here];
- Shipping Method Description: Express;
- Min. Items in Cart: 2;
- Max. Items in Cart: 5;
- Country: United States;
- Click Submit to save the Rule.
Domestic Priority shipping on 6-8 items:
- Shipping Rate Calculator: Flat;
- Shipping Amount: [Enter your C1 rate here];
- Shipping Method Description: Priority;
- Min. Items in Cart: 6;
- Max. Items in Cart: 8;
- Country: United States;
- Click Submit to save the Rule.
Domestic Express shipping on 6-8 items:
- Shipping Rate Calculator: Flat;
- Shipping Amount: [Enter your C2 rate here];
- Shipping Method Description: Express;
- Min. Items in Cart: 6;
- Max. Items in Cart: 8;
- Country: United States;
- Click Submit to save the Rule.
If you will ship Internationally at a different rate, repeat setting up the rules above but select Country: All Countries, which will cover the rest of your chosen Shipping Destination countries that don't have a Rule of their own.