The common mistake is buying a set. A boxed set of twelve chisels costs less per chisel and leaves you with ten you never touch and two that are too soft to hold an edge. Three good ones cover almost everything, and you will know which three after a few months of work.
Where quality genuinely shows
Spend on anything with a cutting edge, because the blade metal is the tool. A chisel or plane iron that will not hold an edge needs sharpening every few minutes and the work suffers. Spend on measuring and marking tools too, since an inaccurate square quietly ruins everything squared against it.
Everything else can be ordinary. A hammer is a lump of forged metal on a stick and an expensive one drives nails no better. Clamps want to be numerous rather than fine, and cheap ones are fine for most holding.
Second-hand is usually better value
Old chisels, planes and saws from before mass production are frequently better metal than mid-range new tools, and they sell for less because they look tired. Surface rust cleans off, handles can be replaced, and a dull edge is expected rather than a fault.
What to avoid in a used tool: pitting on the working face of a plane iron or chisel, since that pitting will interrupt the edge and cannot be ground out without losing most of the blade. Cracks in a casting. A plane body that is visibly twisted. Those are the genuine write-offs; almost everything else is cosmetic.
The order to buy in
Buy a tool when a job requires it, not in anticipation. You learn what you actually need by being stopped by its absence, and the tool you buy then will be the right one because you know exactly what it has to do. A workshop assembled this way is smaller and better suited than one bought in a weekend.
The thing worth buying first
Sharpening equipment, before any additional cutting tool. A mediocre chisel kept properly sharp outperforms a fine one gone dull, so the ability to sharpen multiplies everything you already own. It is also the purchase most people put off longest.