The way ive always handled trade routes, is that you first need to
build a road. If the road already exists, or this is a sea trade
route-- then you dont have to worry about that..

Next, you have to have guilds at BOTH ends of the trade route..
Afterall, you have to have a place to sell all this stuff, right??
The guilds, however, can be level 0 holdings, it dosnt matter..

Also, you will usually get diplomacyed by the kingdom you cross
through, asking for some of the money.. The excuse usually being
tarrifs, or some such.. I generally dont let kingdoms you just pass
through do anything-- unless they actually have a reason to ask for
money-- like they provide protection.. Demanding money for no reason,
in my book, is a non-alignment act for any lawful person. Thus he'd
loose regency. It also wouldnt be good, but non-lawful good person
could possible get away with it depending on the circumstances..

Your question, about having two trade routes back'n'forth. I personally
wouldnt allow that.. I view a trade route as just that-- trading back
and forth, for profit.. However, I dont use the same equation that
the main book does for profits.. I have it 'Average of Source and
Destination Provinces + 1' and round that up. For example, if Illien
trades with Abbatour, he could make 6 GB a turn from that trade..

- --

Of course, to have a trade route, you have to either-- be trading
with a diffrent race, or a diffrent terrain type. I like that rule,
I feel that other type of buisness is represented from the amount
of money the guilds make.. I do, however, have an domain action
for trading that isnt a trade route..

Trade Success: 10+ (or 5+)
Type: Domain Base Cost: 1 GB, 1 RP

This action allows the regant to send needed goods and services to
another provinces. This is a one time deal, if circumstances warrant
you could set up a trade route to the other kingdom. But, if, there
was a large fire that ravaged one of the village, and you happen to
arrive there with cloth, and other supplys -- then you can make
quiet a profit. You can use this action at anytime, but it is only
really useful when the items are needed.

The roll can be opposed by any guild holdings in the province. To do
so, they meerly add the level of their holding to your success roll.
If the items are desperatly needed, then they cannot resist in this
method. The profit from this route, is the same as the level of the
province, divided by 2. If the items are desperatly needed, the profit
equals the level of the province +2. (All numbers are rounded up)

You send some items to illien, hoping to sell them there. The other
guilds, not wishing to give up a second of their market, add to your
success roll. You now have to roll 17 or more to succedd. However,
you spend 6 regency points, and the roll is back down to 11. They
dont interfere anymore, and you sell your items (you made the roll).
The items arnt really needed, so you only make 4GB in profit.

However, lets say that you send items to illien after a large fire.
The other guilds dont bother you, so you have to roll 5+ on your
success roll. You manage to do so. Using the disaster econmy to its
best advantage, you make 9GB off of the shipment.