I am a mix from scratch guy, but if I could find a developer pre packaged that would be great too.
Some of the DiY dry develpper chemical components are getting hard to source without a ton of paperwork as even a company, and cannot be mailed any more, at least in North America. The great war on drugs and terrorism looks down on some of the restrainers that are basically hydroxyl amine (ie nitrated) sulfuric or hydrochloric acid salts. Not quite techinically correct, but you get the idea on why they might be viewed as suspect.
Bleaches can be replenished, and bleaching goes to completion and going a bit longer wont hurt. They last a very long time stored partially used. Mine like on three years now, with periodic replenish and safe disposal of the overflow effluent.
Fixers also can be replenished, and you cannot over-fix a c41 film. They die when they sulphur out, or become saturated, which is no different from B&W fixes, although the pH is likely different from the average b&w film fix.