To answer them in order:
1) I hire an accountant. I live in a major urban centre with a large theatre/dance community, and there are several firms who deal exclusively or primarily with arts expenses. (And all of these accountants are former dancers.)
2) I keep a pencil case in my messenger bag into which I stuff any receipt I plan on deducting. 2-3 times a week, I empty the pencil case and enter it all into a spreadsheet, then I put the receipts into monthly shoeboxes. When tax season comes around, I give the spreadsheet and the receipts to my accountant. It only takes 5-10 minutes a week in total, and it saves me a few hundred dollars.
3) I'm pretty good with paperwork and bureaucracy and accounting, but I've honestly found that hiring an accountant pays for itself. They find all sorts of deductions and credits and loopholes that I would never have found on my own, and so far, having used the same one for three years, these extra bonuses have more than paid for the cost of hiring the accountant in the first place.
4) I live in a jurisdiction where freelance and contract SMs can deduct almost anything which is even tangentially related to the arts, broadly stated, as a business expense. Subscribe to Stratford? Not only can you claim the subscription (it's industrial research, after all!), but you can often claim the transportation as well. Buy a book or rent a movie? More research! Go clothes-shopping? If it's stuff you'll wear to work, then it's equipment necessary to perform your job, so claim it. Have lunch with a friend? Well, if your friend so much as ASM'd a fringe show, that's now a business meeting--claim it! Your union dues and certification courses and professional memberships are almost all claimable...
Sometimes people overreach and get audited ("Now, I'd like to talk about your clothes budget." "Ah. Well, as a stage manager, I need to maintain a large assortment of all-black clothing in order to perform my job, and I consider it a professional expense." "You wear a $300 backless sequinned cocktail dress to your job as a stagehand?") but in general it's pretty much open season. The saving grace of this entire system is that so few SMs make enough money to pay income taxes in the first place that all of these credits and deductions rarely add up to very much.
Of course, a few years ago, the courts found that resident SMs (which includes SMs who are technically freelancers, but work primarily for one company) should be counted as employees rather than as contractors, which turned their world upside-down. (It is expected that employers will provide their employees with all necessary equipment and expenses, while freelancers are responsible for it themselves, so employees are allowed to make significantly fewer deductions.)