Should I turn my oil fired hot water off when I go on a one (1) week vacation?

I don't think that is necessary. I don't turn mine off when I go on vacation, at times for three weeks.

Just turn the temp down. I would turn off the house water though, just in case a pipe breaks.

I disagree. Why pay for the lost of energy when you are not using it? Also, turning off the water to the house is the cheapest insurance you will ever buy. If you would have a leak while you are gone you won't have to worry about flooding from your tank.
Good luck, Tom

I agree, especially with turning of the main water supply.

Since this is oil fired it is probably a combination heating system and domestic hot water system. The savings probably not worth the hassle of relighting, unless there is a "stand-by" setting.