I have just finished 40 minutes of doing 5 courier missons at once and getting the bonuses for all of them. I thought I would help out others to reveal to them how to do multiple courier missons and the pitfalls one might fall into.
Step 1 - the locationFirst you should find a system that has some good agents. I recommend finding 2 lvl3 agents in the same system, preferably of the same corporation, but that is an individual preference. It is useful if the stations also have some lvl1s and lvl2s.
The system is best to be on the edge of a region or at a dead-end system (only 1 jumpgate). This is to limit the jumps required.
An example of a bad system would be Amarr (too many jumpgates, central in region, leads to too many other regions)Step 2 - the shipThe ship should be fast and have a good cargo capacity. If you can't get a fast ship then i recommend using mwds (abs are useless for courier missons). You will probably find that the best type of ship for this set-up is a cruiser. A battleship is not good because it travels too slow in warp and those seconds do add up after a while.
If you can not use a cruiser, or cant use mwds (get them!) then use max lvl2 agents and use a fast frigate with abs and cargo expanders.
My recommendation of race is Gallente, the exqueror with 2 10mwds, cap rechargers and cargo expanders, this is also a cheap ship so it is good for anyone.Step 3 - Know the area!
Before doing multiple agents then i recommend getting to know your area. This involves doing single agents for a while, preferably the ones you will be using when you move to multiple agents. This will get you used to the jumpgate layout and depending on your memory you will have developed a good mental map of the area.
THIS IS ESSENTIAL! Why? because if you get multiple missons then you need to quickly calculate the best combination of jumps and routes that will get you around faster, using the map in the game is slow and annoying, use the map only while you are already travelling just to check your layout. The experience will also teach you the capabilities of your ship.
Hopefully this will change in shiva.Step 4 - Starting out
Do not think you can immediantly start doing more than 2 missons at once, start small. Do 2 missons and see how you go, if you succeed in half the bonus time for both several times then advance to 3, then 4, then 5... I recommend not advancing to 4 until you have been doing the missons for a week or so.
Step 5 - The rushThere is nothing better than what i like to call 'the rush' it is that feeling of adrenelin when you realise that you got 5minutes to do 3 jumps and dock at the station before your bonus expires. Don't let this faze you, I have found that this is the most exciting part of it (yes it seems carebearish

) and it matches the excitement you get when 10 guys are hunting you in 0.0 space.
If you aint careful enough then you will begin to
crave 'the rush' i recommend you dont... it is highly stressful and will soon see you going crazy from the maddening feeling of failure. Occasionally it is good for the multiple misson doer to take time off and go mine.
Finally - The pros and cons.Pro: You will not loose your ship

.
Con: You do not kill anyone's ship

.
Pro: Earns some nice isk and implants.
Con: You dont have time to spend it or use it on anything.
Pro: You get some
very good standings.
Con: High standings one place means low standings in another.
Pro: Lots of good freight items, skills and t2 con items.
Con: You can get them by doing kill missons.
Hope all you people find this useful.