Not an audiophile, don't own any good headphones yet. Is this a good buy to use with the monoprice $6 buds from massdrop for now until two months later when I get a ~$150 headphone?
cccxmomg. if you only have cheap sub-$10 headphones, please upgrade your headphones before dropping $60 on an amp. those kinds of headphones won't benefit from an amp. yes, you can get a really solid pair of $150 headphones. (aka the open Beyerdynamic DT 990 Pro 250 ohms). those would require an amp.
edit: usually most closed (portable) headphones on the market under $400 will not require an amp. you look at the headphone's output impedance to see if you need an amp. anything above 32ohms will benefit from an amp. some people say that they find the sound quality of headphones between 16-32ohms do improve with an amp but I haven't noticed anything dramatic. YMMV :)
cccxmThat depends entirely on your perceived budget. Two years ago I would have jumped on this drop. Now I'm saving up for a Project Ember. At some point I might buy a Bottlehead S.E.X.
Headphones make more difference in the sound than your amplifier does.
That said, yes this would be a good starting point although I'm unsure how the tube is included in the topology of this amp.
No, the monoprice earbuds will not sound good through this. As stated by others, anything with a 16-32ohm resistance will not sound good through an amp.