Regarding mileage, one of the popular references on tax laws (Quickfinder) suggests you sample a week a month, come up with average weekly miles, multiply that weekly average by the number of weeks you work in a year, and call it good.
A couple of comments: First, only your business miles are deductible (and not commuting miles or personal miles). Second, you're talking here about using the standard mileage rate, but you can also base your auto expense on your actual expenses. (Basically, you track all your expenses, calculate your business use as a percentage such as through above mentioned sampling, and then take deduct that percentage.)
For what it's worth, I think that the standard per mile rate is usually optimal. One commonly see people go to enormous work to save an extra, like, $200 in taxes.
Steve Nelson, Publisher, www dot llcsexplained dot com and www dot fasteasyincorporationkits dot com.