176 stars and ready to go

I use these this season right? How many per player? When do I start?

Top level academy and coaches ready to go with a new U20 player

This coming season yes. And players scouted can have a birthday on any of the 7 days, so to be sure a player is U20 eligible the norm is to scout R2 D1, and then R2 D2. The YA scouting week runs Tuesday until Monday so you can scout both the Monday and Tuesday in R2, and they'll both be certain of being U20 eligible.

After that Scout D2 of each round for as long as you have stars, or as long as you think a player could still have a chance of U20 selection. The later they're scouted the less training on 10 nets they can have ahead of the U20 WC, so R6 or 7 is normally as late as people would scout.

Were it me I'd be scouting R2 D1 onward with say 40 stars per player until I ran out of stars.

Cheers, should be able to do 5 x 40 then

Is there a point at which too many stars can devalue a player? I've had better results with 20 and 30 stars than 40 and 50...

thats mostly down to luck although common wisdom thesedays seems to agree that anything past 50 becomes a waste or too much of a gamble

Not devalue no, just for each additiona star above 10 you get a smaller and smaller increase in the chance for a better player.

40-50 stars will thusly give a better chance for better players than will 20-30. But as both will pick from a range in specific instances the 20-30 stars players you've picked could well be better, it's just unlikely to hold true on a wider scale.

There is though a thought it's not worth using more than 50. Using lower numbers of stars allows for more players to be scouted, thus avoiding the risk of your one big scout being a short, light, timid, rebel with no leadership or exp

Also there's now a huge impact from lvl 3 YA facilities. They make more impact I'd think on a 40 star player than would another 100 or even 200 stars.

The numer of stars being used did go really high, and there's reason - http://www.blackoutrugby.com/game/club.squad.php?squad=29&nat=1#player=10150789&nat=1

But in the main people using that many stars returned far too much dross for most managers to risk doing similar.