Here are the combination wrench sizes that you should have
5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4". You are less likely to need sizes larger or smaller then those. In metric 8mm, 10mm, 12mm, 13mm, 14mm, 15mm, 17mm, 19mm.
That would be what I would start with.
Don't take this personally, but thank you for making my point. None, not one, of my current personal bike uses any of these fractional tools. My
A road bike doesn't use any of these metric tools and my
A commuter uses none except the 10mm (box or open). However all my bikes use 4,5,& 6mm hex keys, a pedal wrench, and the commuter uses a 19mm cone wrench for centering the cantis (a 19mm combination is too thick).
My point whether you prefer sets, or buy as you go, do an assessment of what you actually need (and will use) and compare your needs list to the contents of any kit. Then compare the cost of buying loose vs. the set. One other reason I don't recommend sets is that no one maker makes the best version of all tools. You may prefer mostly brand x tools, but for some will vastly prefer Brand Y or Z.
If I look at my selection of tools, there isn't one brand that accounts for more than 20% or so.