Contract Killer: Sniper more accurately described as "Kill, Steal, & Destroy!"
#1 - Do I need a dedicated device and be signed on to the game 24/7?
Yes, if you don't use gold constantly.
#2 - Can I keep up with the game for free?
Yes, but you will spend over 100 hours a week focusing on progressing in the game the most efficient way and without making mistakes.
Time & Real World Money - Obviously purchasing gold game currency, with real world money, is a bit of a gamble because you don't really 'own' anything with it and collecting game cash/diamonds takes a lot more of your time. This game takes a lot of time and using gold reduces the time, which creates the very strange dynamic of paying real money to play the game faster/easier, therefore less time playing, and most importantly, when you want to play. I understand the importance of getting to play the game when you want, without losing your progress, and wanting the opportunity to play all of the game content, but everyone knows in-game cash/diamonds doesn't get you there.
Without using gold, you have to choose between trying to keep up with the game and being competitive in PVP (Player versus Player) or waiting to earn gold so you can play the game (campaign sections) in the programmed natural flow of progression.
For access to all of the game content and/or to simply keep up, you have to earn or buy gold. If you want to play for free and sleep 8 hours a day, you will have to pay attention to this game every moment you're awake. Only using gold earned by playing PVP is a far stretch from reasonable expectations for players. 4000 AP (Assassin Points) for the Global Event's reward of 50 gold means you're paying hourly attention to the game for 13.5 hours a day for 4 days in a row, while winning 3 times every hour and not losing a match. 100 VP (Victory Points) for the League Event's reward of 50 gold, in free-play terms, is almost 17 hours a day.105 hours paying hourly attention to the game per week; that's about 62% of your total time in a week.
Unless there is a constant supply of new players, this game essentially stops due to the lack of variety.
Reminders for people already playing:
7110 AP is the highest possible score you can attain in a Global Event without using additional energy.
Silver League (2500 AP) will take roughly 33 hours of your attention in a 4 day span.
iPhone 4, usually.