As postdoc, you first point of contact will be Meg Rodriguez, our postdoc manager. Check out her website for information about career development and benefits. Employee at the lab are eligible for several discounts including a reduced RSF membership fee and cheaper cell phone family plans (benefits).
As postdoc, you will get your health insurance from Garnet Power including dental and vision care for a very small co-payment.
For any question to your visa status, reach out IRSO. Contact them before leaving the country regardless whether for a conference or vacation. If you are on a J1 visa you need a travel signature which you must renew it after one year. Usually they will furthermore ask you to send them an updated I-94 form, which you can download, after your return to the US.
A lot of information can be found on the tax website of LBL. There is both federal and Californian tax. Many countries have tax treaties with the US which exempt them from federal tax (not Californian).