The cost of maintaining equipment used in your business, whether rented or purchased, may be deductible. Yes, the cost of faxing is an expense. The interest you pay can be deducted, so long as the proceeds from the bank loan were used for business purposes. Yes, legal fees arising from managing your business or producing or collecting income are all deductible. Any license or regulatory fees paid to governments as part of your business are deductible.
Stamps are deductible.
Keep your receipts. Yup, rental payments on your business site are deductible. Again, this is an area where you need to talk to an accountant to make sure you are not deducting a capital expense. Now there are some very particular rules you must follow to get a deduction for travel expenses. So do not think that you are going to convince the IRS that three weeks in the Caribbean was a business trip unless you can prove it.