Welcome to the drop troops!
The most update rules for the Elysian Drop Troops is in Imperial Armour 3 second editon. This has all the pts amounts and except for the
IG codex you don't need anything else. The beacons are called tracking beacons and let any friendly unit
DS without scatter if within 6"...which can be amazing if used well. The vets do not have camo cloaks with the infiltration option so they do tend to be rather squishy. However the infiltrating option can be very nasty if used with finesse and in combination with things like coteaz / assassin or the new raven guard detachment to help you get turn 1. Alternatively beacons are super useful with army wide
DS and alternative deployment options is always nice.
The D-99 drop troops are located in Imperial Armour 4 second edition.
Combat drop actually works for more than valks. Drop sentinels are actually in many ways better combat drop units. Remember though that you need to have something on the table bottom turn 1 unless you want to auto lose every game. This is the true beauty of combat drop valks (which
BTW are extremely hard to
DS more than 2-3 on a table with essentially any models on it). It is extremely hard for most armies to kill a 1-2 DSing valks that are jinking and zooming when being placed to keep them alive. Even valks can stay out of range and
LoS of most of the worst anti air. Personally I prefer to take 2 or 3 valks and at least 1 more combat drop so I can have 2 valks down on turn 1 to keep me on the board.
Elysian drop troops have a few advantages which can make them fairly formidable if they are taken advantage of.
1) 4x plasma company command squad when they use the ignore cover or tank/monster hunter order to buff themselves and any 3x plasma vet squads which
DS near them are extremely damaging. They are even better when you bring along psykers to buff them. I usually just
DS them in and don't bother putting them in a valk even if I purchase them one. This is ultimately your best and pretty much only source of ignore cover so you absolutely must make it count. This is also the single greatest reason that
IMO the D-99 list doesn't cut it against tournament level lists. (note that I have played my elysian drop troops lists against copies of the
GT winning lists and usually win, not against the
GT winners though

)
2) Punisher cannon vultures are amazing in the regular list and in the D-99 list with their BS4 they are just nasty.
3) 130 pts vendetta. This is what keeps the elysian drop troops able to keep control of the skies. There is nothing worse than playing as elysians and running into flyer based list when you don't have enough vendettas to combat them...it is just embarrassing.
Note that if you don't plan on using combat drop I would take allies to for turn 1 presence. The elysians pay for
DS on all their units. Thus any elysian option to sit on the board and take one on the chin is going to be massively overpriced for the job.