Should I physically solder the components to the flight controller, or should I solder the connectors so I can disassemble the model? Which type of connectors can I use? I plan to use XT60 for motors ESC (it's two motor plane) and XT90 for battery connection, but what connectors should be used for other devices like cameras, transmitters, etc?
There isn't a perfect answer for this, although XT60 and XT90 connectors are very popular for batteries. 3.5mm bullet connectors are also common for motors in fixed wings.
Soldering is great if you're short of space (like on a racing quad) but it's not always practical to solder everything, especially in a confined equipment bay in a foam fixed wing (where you could melt the foam). Additionally, soldering can lead to the wire breaking due to fatigue, because the solder creates a hard spot. This isn't an issue for the big power wires, but it can be for small wires, particularly on large models where they could move around a lot.
In theory a crimped connector has more strain relief, especially where one plug contains many wires. Where these are factory-made, they're usually neater than soldering, and are often necessary to squeeze enough connections onto a board. if the equipment comes with them, I'd use them.
The 3-pin servo-plug is a widely used connector for low-power devices in models. It's a too big for a racing quadcopter (and likely to work loose after multiple crashes) but allows you to feed wires through holes in foam mouldings. They're also robust enough to handle being re-connected regularly, if you have to remove your wings for transport. (note that many of the smaller connectors won't stand up to that).
Another popular connector is the 6-pin Multiplex MPX plug. This is commonly used to replace up to four ordinary servo plugs for models with removable wings. One plug instead of 4 saves time and confusion.
I would suggest to solder the critical components and the parts subject to vibrations and mechanical stress and the ones that you are not planning to replace often. Soldering the components always grant a higher level of safety and reliability. You may use connectors on the parts that you are replacing frequently (i.e. the battery). Use high quality golden connectors with proper electrical characteristics, specifically for the battery connectors use 3.5 mm gold bullet connectors like the ones shown on the following pictures:
I would recommend to solder the connectors and to put some heatshrink tube to grant a perfect electrical insulation and to build a safe connection between the cable and the connector.