Yes 290hp is possible with a stock (internal) b18c. That motor can handle around 300whp just fine.
If you using a fmu your not going to be doing much tuning other then playing with your fuel pressure (using an adjustable fpr)..
Not sure where you got your timing retard number from, but you'll need a btm (boost timing retard) that retards your ignition timing per pound of boost, if you plan to do that..
Or you can avoid all that headache and go with something thats actually tunable such as hondata.Then have it tuned to for more power and reliability.
Depending on the turbo's size (you mention t3t4 so it cant be to huge) you can get away with running more then 7psi and making more then 270 - 290hp..
It's all up to you though and what you want...
I ran hondata and a moderate sized t3t4 on my b16a, made around 280whp running 13psi. I dyno'd @ 248whp running 9psi (whp and hp are different)