In all of the builds I have done, I always went a little farther with them than I intended too. So I plan for that.
I've always built cars in stages with an overall goal. On my Z28, I wanted a fast car (130 trap speed on street tires) that could do everything well and have no issues being driven across the country reliably while still maintaining good street manners.
So, I started with basic engine bolt ons, then suspension/brakes, then more engine stuff, then reliability stuff, then more engine stuff and currently, more reliability stuff.
Decide what you want and want you may want in the future and plan ahead. As you mentioned, no point in buying parts several times, do it right the first time.
99 Chevrolet Camaro Z28 M6 - 6.676 @ 103 in 1/8, 10.512 @ 130.2 on street tires, H/C/I
93 Eagle Talon TSI AWD 5spd - Built 6 Bolt, 16G Evo3, HKS 272 Cams - under construction
94 Mustang GT - 5.0 bored and stroked to 347, Vortech V1 @ 10 PSI, Tremec TKO 600 - PIA