Welcome,
To start, make sure you have a firm understanding of the fundamentals of electronics and electricity. Be aware of the potential dangers and hazards of electrical and electronics repair and troubleshooting. With that said, the best place to start would be eBay and/or Amazon. You can find most of the basic tools you would require here and at a reasonable cost. Once you advance to more complex repairs and designs you could start to look at specialty test equipment companies such as TEquipment, Davis Instruments, TestEquity, Test Equipment Depot and etc.