Richard,
If the amp is new the tubes should last many thousands of hours....do not leave the amp on 24/7 but leave it on the day you listen and turn off when done for the day...try to avoid, on-off, on-off on days you listen...tubes are like light bulbs and on-off can stress them. I would not buy any extra tubes right now. Wait till you get used to the sound and then experiment with tube rolling to change the sound of the amp....not every tube in the design has a sonic effect on a change...you have to know which ones will make an impact. BTW what is the amp?
If the amp is new the tubes should last many thousands of hours....do not leave the amp on 24/7 but leave it on the day you listen and turn off when done for the day...try to avoid, on-off, on-off on days you listen...tubes are like light bulbs and on-off can stress them. I would not buy any extra tubes right now. Wait till you get used to the sound and then experiment with tube rolling to change the sound of the amp....not every tube in the design has a sonic effect on a change...you have to know which ones will make an impact. BTW what is the amp?