Note the bolded parts of the quoted post.
Without reads I don't think we can just assume that BTN is not raising for valuer due to his raise size. I would happily raise this size with my whole range and don't stick to any "standard" sizing.
If his opening range is 9 percent how much of that do you think he will fold to a 3 bet from a blind? I think he is going to 4 bet or call most of it.
Looking forward to postflop when we 3 bet and get a caller. The pot will be about 600 and we have ~1200 left behind. What's the plan when these overcards hit? Most of the overcards are in his 3 bet calling range so do we just give up?
When you say it leaves only the bottom of his opening range do you think he is going to 4 bet the majority of his opening range?
How could you possible say that we do not have any read, we have pretty decent size on villain ~1,5k sample which show us that he is opening on late position 9%. Only thing which we does not know (does villain plays linear range late position+early stage or more creative range, since i know many good tight players plays early stage on position creative). Ofcourse can not ignore hero image (how villain sees hero), since hero has 1,5k sample it means villain has approximately the same sample on hero and this can affect the decision.
In general opening size should be more then 3bb, since there is 1 limper+2 active players+ante. Therefore this opening is weak from tight player part. Basically villain took the pot control and assuming to have at least one caller not a 3bet! Which reflect villain true hand range pretty clear, (villain got bottom of his range most of the time+creative range) if villain decide to call. Villain weak opening screams to see cheap flop. And when villain really does have good preflop value hand he/she will 4bet (but this is really small part of possible range)! And if villain really does have bottom range or creative opening range he/she might will just fold or call it! And if he does just call villain has most likely postflop value hands (connectors, mid high cards etc rarely his top range).
"Looking forward to postflop when we 3 bet and get a caller. The pot will be about 600 and we have ~1200 left behind. What's the plan when these overcards hit? Most of the overcards are in his 3 bet calling range so do we just give up? "
It is really hard for me to answer, since the decision is strongly correlated with hero image+flop texture! All we know that villain most likely range is now overcards, which means we should give up the hand if situation is going to be hot! But note that if villain is calling (we know now his opening range is 2 high cards most likely), this will be negative expectation for villain overall since hero have pretty clearly defined her/his hand strenght on preflop and villain still decide to call!
If you think about what villain thinks when he/she facing against strong 3bet preflop, what kind of hand range could possible villain but BB if we can assume that hero is solid player (i do not know nothing about hero just assuming)? (hero hand range is more polarized then villain range). It makes even harder villain to continue very bottom of his preflop opening range which he/she is representing preflop. imo
"When you say it leaves only the bottom of his opening range do you think he is going to 4 bet the majority of his opening range?"
Most likely villain does not 4bet in this situation assuming he is solid tight player and knows what he/she doing! imo
Summary: On preflop: 3bet or fold (depends on villain), but calling OOP (vs ~9% range)+possible multiway is suicide for weak made preflop hand, since hero basically set mining that point and we can not assume that implied
odds are there (villain is tight - we do not have more info). imo