First Tube Amp: Advice? Keep spare tubes on hand?

THANK YOU!
All well reasoned, excellent replies.
When you say decide whether I like the amp first, you mean after the break in period?
The amp is a relative cheapie. I am almost embarrassed to say it. Please remember this is my first foray into tubes, so I decided to just dip a toe rather than jump into the deep end. It is an Onix SP3, which I have read favorable reviews of.
I got a great price on it.
It is a manual bias unit.
I do know my way around a multimeter.

Yup, I love all you guys.
Is this any way to run an airline?

Again, your replies are concise, well reasoned and very much appreciated.
I posted under a new thread about a problem(?) I'm having.
The bias on my new amp is specified at 1.5 volts. The left side will not bias above 0.5.
What should I do and/or not do?
Help me, oh help me please.

Again, thank you all mucho.
I have spoken to the manufacturer and they are sending me a shipping label to return this one and are sending me another.