You want to give away a whole planet for a single ship? why that?

It seems I missunderstood. Well I am a noob.

reagrding the home planet of cargo ships: in my experience, the easiest way to handle those is to add the planet you want to designate as their home planet to the sponsor list of the shipyard where you build them. the game will ask you which of the planets in the sponsor list should be the home planet. the planet doesn't actually have to contribute any manufacturing points to the shipyard and the distance of the shipyard doesn't matter.

this way you can build the cargo ships on a dedicated manufacturing planet and assign the "trade planet" as their homebase the moment the ship launches from the shipyard. 

i don't think there is a way to redirect existing routes, though.

some general pointers regarding trade:

the bonus from the trade capital is really huge - it seems pointless to make routes that don't use the trade captial as the homebase, so it's probably a good idea to decide early on which planet will be the future trade captial and assign that planet as the homebase of all your trade ships. the trade capital and trade post scale with wealth adjacency bonuses, so it's a good idea to use a planet where you can put a few shopping centers, a bank and maybe also the economic capital adjacent to the trade capital and/or trade post - all of those buildings will boost each other. put the planet on 100% wealth after the infrastructure is built up. that planet alone can fund your whole empire, so every other planet can run at 0% wealth.

trade income scales with the length of the trade route i think, so it's probably a good idea to use some planet that is far away from your trade partners.

don't really know what factors affect the trade route output. i *think* distance matters, but not really sure if the population or wealth output of the planet has any effect. wouldn't hurt if we had some map filter/overlay that shows the potential trade yield of each planet. as it is now, i usually send my trade ships from my trade capital to alien planets that are far away. 

also, the default trade ship design is horrible. it's full of life support systems and no engine, so it moves across the map at a whopping 2 or 3 tiles per turn. i like to make my own design for cargo ships. cargo module, 4-6 engines, some life support - this way they'll actually get to the target planet before the game is over  

Well, now I have another one:

4. Is it possible to attack ALL ships in a hex. Drengins are right now protecting their fleets by splitting them into single ships. That way I allways have to attack the same hex (only single ships against my fleet every time) several times and when my movements points run out, the blasted Drengins take the rest of the ships in that hex and run.

One of the XML files is called TradeRouteDef. If I'm reading that file correctly, a standard or slave trade route should have a base value of

0.05 * [planet "incomes"] + max(1, min(250, 0.025 * [trade route length])) + max(1, min(250, 0.1 * [trade route age]))

A luxury trade route should have a base value of

0.1 * [planet "incomes"] + max(1, min(250, 0.05 * [trade route length])) + max(1, min(250, 0.1 * [trade route age]))

Luxury trade routes should additionally grant +5% influence and morale to the host colony, while slave trade routes should grant +5% production to the host colony. All three types of trade routes should grant +1 morale to the colony if at least one of the empires involved has the Entrepreneur faction trait. This base value is then multiplied by the trade route value bonuses which apply to the planet in question.

It should be noted that the "planet income" modifier listed in TradeRouteDef.XML appears to be based off of planetary production rather than any specific to planetary income. I have a (somewhat modded, but nothing specifically aimed at trade routes) test game where Earth is specialized for manufacturing and has a population of 61.4 (production of ~109) with -39.5 income while another world is specialized for wealth and has population of 27.5 (production of 61.9) with 2070.8 net income, while Drengi (my trading partner) has a population of 17 (production of 22) and a net income of 11.3. The Earth-Drengi route 6.6 of its base value from the incomes of Earth and Drengi according to the tool tip for the trade route in the Govern screen, while the other colony's trade route gets 4.2 of its base value from the incomes of my other colony and Drengi (again according to the tool tip). 5% of 2070 is 103.5, so clearly net income is not used to compute the bonus from trade planet "incomes," but 5% of 83.9 (22 production from Drengi + 61.9 production from my colony) is 4.195, which is rather similar to the value of 4.2 listed for that trade route's bonus from trade planet "incomes." Similarly, when we check Earth-Drengi, we see that 0.05 * (109 + 22) = 6.55 and that the Earth-Drengi trade route has a bonus of 6.6 from trade planet "income." Note that if you have structures (or projects, if you've modded the existing projects or added new ones) giving bonuses to gross income (e.g. v1.01 Prometheon Pleasure Parks), this bonus will NOT affect the trade route value.

This indicates that the best trade worlds are high population worlds, preferably with bonuses to base production (high approval, stacked Economic Rings, Durantium Refineries, Thalan Hives, perhaps a few other things; note that despite v1.02's renaming of the tool-tip to indicate that the Durantium Refinery and probably everything else that gave production bonuses give bonuses to "total manufacturing," the structures themselves still give their bonus to a planet's base production before any modifiers) and trade route value multipliers.

This also indicates that trade on smaller maps tends towards pointless; smaller maps cannot accommodate long trade routes, and tend to be relatively short, which imposes several constraints on the two main contributors to a trade route's value. It just isn't feasible to make up for significantly shorter trade route lengths by way of population, not when only 5% of the planetary production goes towards the trade route value and planetary production values tend to be in the low hundreds at most anyways.

This would appear to me to be a very good rule of thumb, though I'd also tend to prefer higher-population worlds if they're similarly distant.

AFAIK for #4 and #5 - no and no - trade is defined as inter-civ not intra-civ - pirates can destroy your freighter en route and enemies can attack the freighter to destroy it

The reason for #7 is probably because they want to avoid the exploit / bug where a ship enters the dry dock and the game crashes because you don't actually have the strategic resource to build it.  The whole strategic resource system is new (I think) in GC3, so there are some rough edges.  For the moment -- I suggest not queuing up so many ships in advance on your shipyards.

Thanks a lot wuphonsreach and joeball123, that really helps me a lot. A final question then, where do I find BattleBehaviorDefs.XML? Ive tried searching my HDD for that file and the net and come up empty handed.

Thanks, found it. Is it possible to add another, lets say Artillery, by copying and editing, without the game falling apart?