A revived "old Pentax K1000" is not likely to be all that precise in terms of shutter accuracy and meter accuracy. Exposures will likely be within a stop, but you really can't bank on anything more accurate until you test it.
My suggestion is the start off with a 3 shot bracket, one stop over to one stop under. Do this for at least part of the first roll and for any really important images on the rest of the roll. When it's processed you can judge better whether you need to continue with 3 shot brackets or not and whether the "normal" exposure is more often the correct one or whether you need to bias your exposures one way or the other.
Velvia 50, like all transparency films, has a rather narrow latitude and contrasty scenes need to be very carefully exposed. Even so, if you are only looking at needed enough dynamic range and overall image quality for screen display then you can get away with some pretty bad exposures provided your scanning and post processing skills are good enough.
