One TP/SL can be set on server per ticket.
OrderClose() can be used to close part of a position as you see fit.
Yes, absolutely. "Stop loss" and "Take profit" are not an order type, they are a concept which implements stop and limit orders. In practice, a SL is a stop order and a TP is a limit order. You can place multiple stop orders and multiple limit orders respectively. In order to reconcile the position you will then need to use "CloseBy" (on hedging accounts).
Ugh... it was on the front page... Someone was blasting the forum and mods must have deleted the duplicates.