To actually do anything, you will need some stuff called ’test equipment’. Can’t go wrong with pieces from Fluke, Hewlett / Packard (now Agilant), Tektronix. I prefer the old stuff, 30-50 years old. Better built, mostly repairable, great ’feel’ to the knobs.
Easier to use, too - unless you like scrolling through layers upon layers of windows and screens. And more accurate unless you spend a king’s ransom - but then, the old stuff cost a king’s ransom back in the day. My old Tek storage oscilloscope cost more than the big Mercedes when new.
You will need a power supply, multi-meter, oscilloscope, and signal generator, all lower bandwidth stuff since you’ll be doing audio. Low bandwidth is cheaper too. And a good soldering station (solder / desolder) is useful - don’t scrimp, get a good one. Best in my experience, which includes the better known brands, is JBC made in Barcelona, available from Accessotronic.
As for projects, consider the J.L Hood class A amplifier for Quad ESL’s. Very simple and pretty design, good and clean sound, easy to make and very easy to try out different types of components for their sound. Sanken transistors make them sing.
Welcome to DIY !!!