Biggest advantage of missions in High Sec is no PvP - eg. you can only lose ships due to disconnect or bug. Missions are always there so only drawback is fly time and killing mobs time. Fly T2 or faction fit, but expensive faction attracts gankers, so T2 is cheaper, safer and better in DPS.
Ship to use - Rattlesnake, Golem or Paladin - tanky, lots of DPS, and can use micro jump drive.
Secrets of Missions - the biggest payout is not ISK/LP reward from agents but drops and bounty from missions. Actually there are only three missions worth doing : Silence the informant, Enemies Abound 3 and Gone Berserk ( the last one is not worth farming but worth full clear )
Silence the Informant drops 5 Elite Drone Tags in first pocket - about 35m ISK in total
EA 3 drops about 65m in tags - it will drop your standing towards Gallente into “abyss” quite fast. Small drawback.
Gone Berserk - 25m in bounties and loot
Each of them takes 10-15 minutes to finish.
After Downtime they reset so you can do them again.
“Blitz missions” - those you do and complete after you got them eg. no daily farm - are - Right Hand of Zazzmatazz - drops sometimes 50-70m implant, Stop the Thief and Cargo Delivery. The “Blitz missions” will push your standing higher and reward you with LP.
Best area of operations is Lonetrek from Torrinos System towards Oipo system ( 5 systems in total ) where you have 7 agents.
In average you always have 5 active missions of the first 2, which is 220m ISK per hour of casual gameplay, without constant Dscan and other ■■■■■■■■.
I got so rich that I was supplying three accounts and was buying faction ships and even a citadel just for fun. Then I got bored and quit.