A few simple questions i guess :]

Hi i am knew here hehe :D
i am working on a map now... and i want to put a trade system wich is like in silkroad if anyone of you have played...
So the idea is that a user can buy a horse or a kodo wich will carry the items (items with no effect), so the user buys a couple of items in one shop than he travels to another shop sells it there for a higher price let's say ii bought something for 100 i sell it in another shop for 150+ (if i sell it in the same shop i bought from i will only get half price)

now also there are 2 types of items carriers
horse - normal hitpoints, fast movment, and only has 4 slots in the inventory
kodo beast - high hit points, slow movment, and has 6 slots in the inventory (defualt)

so for the questions list:
1. how do i make this Buy-And-Sell-For-More system...
2. How do i change the slots in the inventory...
3. how do i able to user to buy only 1 item carrier, it can be a horse or a kodo.
4. How i make the horse/kodo to auto follow the user after the range betwen them is higher than X.
(for follow u can order the unit to right click the user).

I'll be happy if u would help me with this problem :]
Thanks in advanced

1. This is sort of complicated, it depends on what exactly you want. Is there only 2 shops, or are there more? If there's more, then you need to establish what item will sell for how much at what shop (tons of stuff do to). If there's only two, you can detect which shop the item is being sold at and reduce/increase gold depending.

2. Object Editor...

3. You could use food limit, or if you're already using that, store the item carrier once bought to a variable, then detect if that variable is null or not when the player buys another item carrier. If it is, reject the 2nd item carrier and give back gold

4. When the item carrier is bought, you can simply order it to follow the hero. Therefore, it won't go far anyway.

edit: You might want to start off with something easier if you can't figure out number two.

Thx you helped alot..
ok now
for 1. for now i want to work with 2 shops, and i yes i tried to do what u have said in the triggers but i find it confusing can u explain more?
for 2. i guessed it sepuse to be in object editor.. but still where in the editor...
3. that is one simple idea i didn't think of XD
4. the problem of 4 is that if i order the item carrier to go some point it will stop auto following..and i can't make him unselectable because than how am i sepuse to sell the items?

Thanks again :]

EDIT:
Yay i have managed to create this system... i'll need to work abit more but i got the main idea... i did that instead od just selling the items there will be a passive unit wich has the ability sell (once u click it will sell all possible items in the kodos inventory) so i did that once sell abillity is being cast, check wich unit did this spell and acroding to the unit it will aprove different items... i named them dude1 and dude2 XD..
i did a loop action: from each variable "Slot" (integr) from 1 to 6 check if the item wich is in the slot being check is equal to the one of the items... and so on.. for each item give X gold to the owner of the kodo :D

i also have found the inventory thingy in the object editor :]
now all is left is 4. if you know of The black road RPG there is a wisp wich auto follows ur hero even if u order him to go some point and not to follow again... i need to know how they did it :S any ideas?

Just detect (using triggers) whenever the item carrier is issued an order by a player, and then re-order the carrier to follow the hero.