I have generally just bought what I needed as different tasks became necessary on my bike. Those tools will of course be different for different bikes. I generally agree that it's worth buying "better rather than good enough", but sometimes that depends whether you're buying something that will be used once a year or every week.

I bought a set of combination wrenches to fit my bike: 15mm for the hub nuts, 14mm for the seat post clamp, a pair of 10mm for the brake reaction arm. Floor pump, tire levers, grease, thin oil, and chain lube are pretty much essential. A metric allen wrench set is widely useful (especially 4mm, 5mm, and 6mm wrenches). Screwdrivers and measuring tape are always useful, though you might have those around the house already. Rags! A ratcheting socket wrench and metric socket set is handy, especially in tight spaces.

Over time I picked up cone wrenches, a chain tool, chain wear indicator, spoke wrenches, cable cutters. Then there are useful supplies, such as nitrile gloves, solvents like isopropanol and odorless mineral spirits, zip ties...

But mostly, get a good repair manual (the Park Tools Big Blue Book is pretty solid) and figure out what tools you'll need for a given upcoming task, and then go buy those. No point in investing a lot upfront in crank pullers and bottom bracket tools or headset presses or whatnot if you never end up doing any work in that area.