refinishing the tub

Just some general advice please – the tub is looking tired and I was considering sanding it to bring back some luster to the wood.
I was planning on using an orbital sander and wooden sanding block. I have not oiled the tub and is this something I should be doing at least on the outside?
If so, what oil do you recommend?
I recommend to let the tub dry and sand with medium and fine grit.
Then, we recommend the application of a water-repellent which is colorless, matte finish and will not block the wood aroma.
It is a non-coating treatment and penetrates in the wood fibers letting it breath (like “goretex” for fabric…).
We recommend to finish the Hinoki tub with water repellent
KIHADAICHIBAN (preservative agent for wood) :

a) 7,000. JPY / 1L + 4,500. JPY (Packaging + EMS) + Paypal fee = 12,000 JPY
Please let me know.
Best regards,
iacopo torrini