The greatest difficulty with 4-star is the high entry fee followed closely by the 3 HQ items you need for the books. Past that, the rest of 4-star crafting is much more forgiving. Any non-crafter/gathering item, you can start with 50% quality. You can endure a lot of RNG fail and still HQ. Or, you can spread out your NQ subs amongst other synths. Let's say you were making a set of Kirimu gear, and you got 9 HQs/5 NQs. Use 2 NQs on body, 1 NQ on others. All synths would start with like 40% quality. More than enough to safely HQ them all.