Tool sets, by and large, are really necessary at first. The only specialized tool you might need is a concave cutter. Regular scissors, wire cutters and other improvised tools can be perfectly adequate at first.
Also, by and large, the tool sets sold online and at some bonsai retailers aren't really worth the expense, as they are mostly cheap Chinese-made. Buying a complete set of tools right off the bat isn't the best way to get tools.
Buying really good Japanese tools one at a time over the years is the most cost-effective and useful way to get them. Quality Japanese tools are built to last a very long time. They're also precision-built with edges that cut cleanly (an important quality). They also work better mechanically, with pivots that don't come loose, etc.
If you buy a complete set, you will probably spend the equivalent of what a single good-quality Japanese-made concave cutter costs. Also if you buy a complete set, you will also probably find yourself replacing all of it sooner rather than later, as they break or lose their effectiveness.
