As noted above, 400' is fine. Mexico is the only place I've ever needed a full 400' to reach a main line. They have some big caverns there with the lines placed far back in some of them.
Offshore, you need a fair amount of scope to get a bag on the surface from 200 or so feet in a strong current, especially if you encounter currents in two different directions.
Most of the cave "primary" reels hold 400' of #24 line, and you can add a bit more length if you go with number #18, line, or for wrecks you can go a bit shorter with #36 and get more abrasion resistance, but a 400' reel works well with any of the above approaches.
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The Salvo/Light Monkey/Halcyon reel is a fine design relying on minimum clearances to help prevent birds nesting the reel, and 99% of the time it works just fine, but that last 1% will be almost impossible to clear under water.
The other approach is the Larry Green / Ralph Hood designed reel. It is also a side handle reel but uses a very open design to make it easy to stop and correct any incipient birds nest that may occur. Personally, I prefer this design as you will bird nest a reel sooner or later, and I'd prefer one that lets me clear it quickly under water.
With both of the above designs, I find I can hold the reel in my left hand along with the light holding the reel at about a 45 degree angle to let the light shine forward, then reel with the right hand - that prevents the light dancing around and creating any distractions to the team. And again with both reel designs you can easily control tension on the spool with your fingers.
Way back in the day I used a Reef Scuba reel, and at the time (early-mid 1990s) they were pretty cutting edge, but they are hold tech and not as user friendly as other side handle reels available today, are less amenable to modern light heads and goodman handles and are not as easy to control tension on the spool - but they remain popular with many divers.
