I've seen many questions and answers regarding how to draw tiled maps but I can't really get my head around it. Many answers suggest either loading the visible part of the map, or loading and unloading chunks of the map. I've decided the best option would be to load chunks, but I'm slightly confused as to how this would be implemented.

Currently I'm loading the full map to a 2D array of buffered images, then drawing it every time repaint is called. Q1: If I were to load chunks of the map, would I load the map as a whole then draw the necessary chunk(s), or load & unload the chunks as the player moves along, and if so, how?

My second question regards the camera. I want the player to be in the centre of the X axis and the camera to follow it. I've thought of drawing everything in relation to the map and calculating the position of the camera in relation to the players coordinates on the map. So, to calculate the camera's X position I understand that I should use cameraX = playerX - (canvasWidth/2), but how should I calculate the Y position? I want the camera to only move up when the player reaches cameraHeight/2 but to move down when the player reaches 3/4(cameraHeight). Q2: Should I check for this in the same way I check for collision, and move the camera relative to the movement of the player until the player stops moving, or am I thinking about it in the wrong way?