All you really need is a switch for each mission and a few variable to figure out the success rate. Eight Variables should be enough to completely figure out everything you need.
S1: Timer
S2: Fight Bandits
S3: Steal Treasure
S4: Play Tetris
V1: Mission level
V2: Hired level
V3: Your level
V4: Random
V5: Success rate
V6: Class
V7: Completion time
V8: Time
If V3 => 10 then
Label: mission
Show choice:
>Fight bandits
If S2 = OFF
V1 = 10
Show choice:
Bosly Lv 11 Warrior
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 11
V4 = RAND (1-5)
V6 = 3
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +1000
Change Item: Potion 15
Switch: Timer = OFF
Switch: Fight Bandit = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Bosly hasn't come back from his mission yet.
No:
Goto Label: mission
Kris Lv 8 Thief:
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 8
V4 = RAND (1-5)
V6 = 4
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +1000
Change Item: Potion 15
Switch: Timer = OFF
Switch: Fight Bandit = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Kris hasn't come back from his mission yet.
No:
Goto Label: mission
Greg Lv 12 Summoner:
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 12
V4 = RAND (1-5)
V6 = 2
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +1000
Change Item: Potion 15
Switch: Timer = OFF
Switch: Fight Bandit = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Greg hasn't come back from his mission yet.
No:
Goto Label: mission
Else
Show Message: You've completed that mission.
>Steal Tresure
If S3 = OFF
V1 = 20
Show choice:
Vosh Lv 16 Mage
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 16
V4 = RAND (1-5)
V6 = 4
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +5000
Change Item: Potion 99
Switch: Timer = OFF
Switch: Steal Treasure = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Vosh hasn't come back from his mission yet.
No:
Goto Label: mission
Sommy Lv 19 Thief:
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 19
V4 = RAND (1-5)
V6 = 2
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +5000
Change Item: Potion 99
Switch: Timer = OFF
Switch: Steal Treasure = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Sommy hasn't come back from his mission yet.
No:
Goto Label: mission
Tipp Lv 22 Ranger:
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 22
V4 = RAND (1-5)
V6 = 3
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +5000
Change Item: Potion 99
Switch: Timer = OFF
Switch: Steal Treasure = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Tipp hasn't come back from his mission yet.
No:
Goto Label: mission
Else
Show Message: You've completed that mission.
>Play Tetris
If S4 = OFF
V1 = 5
Show choice:
Bess Lv 4 Mage
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 5
V4 = RAND (1-5)
V6 = 2
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +5000
Change Item: Potion 99
Switch: Timer = OFF
Switch: Play Tetris = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Bess hasn't come back from his mission yet.
No:
Goto Label: mission
Epie Lv 5 Barbarian:
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 5
V4 = RAND (1-5)
V6 = 5
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +5000
Change Item: Potion 99
Switch: Timer = OFF
Switch: Play Tetris = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Epie hasn't come back from his mission yet.
No:
Goto Label: mission
Sipp Lv 3 Ranger:
Show choice:
Yes:
V7 = 600
Switch: Timer = ON
If V7 =< V8
V2 = 3
V4 = RAND (1-5)
V6 = 1
V5 = (V2 / V6)
V5 = V5 X V4
If V5 > V1
Show Message: SUCCESS
Change gold: +5000
Change Item: Potion 99
Switch: Timer = OFF
Switch: Play Tetris = ON
V8 = 0
Else
Show Message: FAIL
Switch: Timer = OFF
V8 = 0
Else
Show Message: Sipp hasn't come back from his mission yet.
No:
Goto Label: mission
Else
Show Message: You've completed that mission.
Then have a common event with:
Trigger: Switch: Timer = ON
Wait 20
V8 + 1
Success works by taking the level of your hired guy, dividing it by his class, then multiplying it by the random number to see if it's larger than the mission level. Keep in mind that the larger the V6: class variable is, the harder the mission will be. With the example you have a slightly less than 50% chance for success, however if V6 was set to 2, you'd have over a 60% chance of success. Also, obviously higher level characters will dramatically increase success rates. If the character was level 12, and class was 3, there would be a 60% chance of success. 12 and 2 and there would be an 80% chance of success.
If you look at the mage in Steal Treasure you'll see he's level 16 and his class is 4. This means that 16 / 4 = 4 X V4, meaning you'll end up with 4, 8, 12, 16, 20 as your possible outcomes, to succeed you need 20 or higher since the mission level is 20, so the mage's chance of success is 20%. You may want to use larger numbers to get more accurate amounts (I would personally increase all the numbers by a factor of 10).
A higher V4 variable, RAND (1-100) for example, would give you many more outcomes which means that your chances of success increase in smaller amounts but MANY more times. To help keep yourself from guaranteed success, increase the mission level or make the increases in increments even smaller. So instead of 16 / 4, it'd be 16 / 6 or 8. Or as I suggested earlier 160 / 6 and make the requirement 2000.
I know what you're thinking, why have 2 variables to determine the success when RMXP ignores decimals? Well, it has more to do with flexability. You can change the numbers just slightly to change your odds of success and it gives people a baseline for comparison since you're using an easily see-able variable (the hired guy's level).
On the timer, make sure the common event is a parallel process if the switch to trigger it. At V7 = 600 and a wait time of 20 frames, it should take 10 game time minutes before the mission is completed. If you want to have multiple missions going at the same time you'll need a new condition branch for each mission and a switch of each mission until you hit your limit (which will be 4 if you're using the standard text interface) and a new common event for each.
I hope that helps you a little bit in the actual eventing. As far as I can tell that should fulfil everything you need for the missions, the only downside is you can only have 4 mission at a time based on your character's level. I'd see about trying to make a custom menu system to handle all the mission availability, but otherwise this should work just fine. Also you'd need another conditional branch for the payment part of it, but I just wanted to get an example going for you.