I think that you would be taking a totally needless risk if you used an AWD number that was not from your own company. While clearly I do not know anything about your company or how they handle car rental reimbursements, I do know that companies negotiate rates with the car rental companies, and expect their employees to use the appropriate AWD number to obtain the negotiated corporate rate. The big question is, if your company will reimburse the rental charges to you, based on their negotiated AWD number, then why would you care to use another AWD number? Bottom line, if you use another AWD number, your company MIGHT not reimburse you, because they did not do the research to figure out whether the AWD number you used will yield a higher or a lower rate, and why should they? They have their own rate and AWD number for a reason, USE IT, or do not use it, at your own peril.

Yes, you can use the Farmer's AWD number since you are a Farmer's customer, and if you are ever asked (doubtful that an Avis employee will ask you about your eligibility to use the Farmer's number), just show them your Farmer's insurance card.

As far as whether or not you need to buy the additional insurance coverages, PROBABLY NOT, but every insurance policy is different, so to protect yourself, either call your agent to ask, or look for the correct section of fine print in your insurance documents. Also, for the rental, use a credit card that covers for rental cars, meaning most Platinum Visa and Mastercards offer rental car insurance coverage for at least the deductible, and sometimes as much as the full value of the rental car, up to $25,000, $30,000, or the highest I have seen, $40,000! Of course, YMMV!