1) usually we slope battered ends 15 degrees (from the vertical). This is usually a detail requested by clients/local designer as they think that it would be more comfortable to sit inside. Actually, because the water makes the body float, the back assumes a comfortable angled position regardless of the tub end. From a functional point of view, straight is same as sloped. I recommend to choose the sloped option if you like the look/shape or to save a couple of gallons of hot water. The bathtub cost is same for the two options: the straight back requires less work but more material, the sloped detail involves more work but less material.

2) Yes, shapes can be customized, anyway irregular or complex shapes are not recommendable because the water pressure would cause structural problems and leakages to unbalanced shapes. We can do square, rectangular, round, ellipse with straight sides, exagonal/octagonal (depends on the size, please consult)

3) please refer to our FAQ`s. There is really no magic solution as wood is best preserved in a well balanced environment. Use the tub often (everyday is best) to maintain an optimal humidity level and avoid cracks/leaking.
For the same reasons, be sure not to use heating systems or central air conditioning in the bathroom, when the tub is not in use (empty)
To avoid insurgence of mold, open the windows after the tub has been emptied and if the weather is very humid, wipe the tub with a bathtowel after use.