A few tips of advice:
1). For advertising, if you have a surplus cash flow left from your old job, yes... hire a cheap advertising agency for your first couple months.
2). Use a groupon based sponsor website that splits part of your deals, it will work wonders for you (put a limit on how many coupons can be bought at first and make sure you can cover the work). For example... I'd start out with 200 coupons and make them good through the next 4 months. Make sure you can get at least 1-2 detail (full) in a day if at all possible, don't overbook yourself, looks unprofessional.
3). Yellow pages is a must, as well as making sure you're in the newspaper each week.
4). If you don't have the overhead covered right now, look at a small private bank loan or small business loan for like your overhead-- make a list of supplies and costs to show them you're serious.
5). If you can go mobile, DO IT! It's a huge benefit and will expand your business.
6). Have your website allow for membership privileges and give discounts for members.
7). Do monthly specials
8). COLD CALL your old customers, document the last service they had and if it was a wax, follow up in the 3-6 month period where they'll need another and see if they'll take it. (Follow ups let customers know you care and will get you repeats).
9). I personally don't advise for you to use fliers on car windshields, however... door hangers with coupons are a great and friendly (non-obtrusive) way to get your name out there.
10). Don't set yourself up for failure by quoting impossbile time frames. Only bring it up if the customer asks. That way, you don't dissapoint (customers will like you more for this reason).
11). You must get insurance, it will save you at some point. Even the best can't prevent underlying weak paint from flaking or a DA/Rotary buffer gone wild, or a random pig tail (it will happen at some point--possibly, hopefully not :xyxthumbs

.
12). Have enough towels and pads that you can do multiple jobs in one day should the opporunity present itself.
There are tons more, but I'd rather not assail you to death by being verbose. Anyways, have fun and good luck! I've yet to start my business, but unlike you my Mrs. doesn't seem so supportive haha. Let us know how it goes. Just remember that this job is like being a salesman "you get out of it what you put into it!"