No kidding? I am happy to hear that.

If the cherry trees are in full bloom at that time, you definitely should take a trip through the Yoshino Valley. It's in the southern part of Nara prefecture, easy to get to from Osaka, and has tens of thousands of cherry trees. One of the best places in all of Japan to see them.

well the museum opens at 8:30 so setting out from Osaka at about 7am would get us there for the opening. I just looked up some info on the museum and it is a huge place, especially if you include the park and surrounds.

Don't push yourself or overbook yourself. I have taken tours with people that wanted to do that...to see EVERYTHING...and after a few days everything started looking the same...because it is SO different.

you will be here in time for Sakura?

Then I suggest not to miss Kyoto: Philosophers Path, Botanical Garden, Arashiyama, and Yasaka Shrine , among the places where you can watch some great sakura. Usually in Yasaka they have light-up there until around wee hours in the morning. The big sakura ( forget the name ) is being lighted, its really really beautiful so don't forget the tripod.
Arashiyama, don't miss out the place its really amazing there on spring.

If you are going to Osaka Castle, try to pass by Sakuranomiya also. Just outside the station is the river and both side of it are all Sakura trees. The place is full of people till wee hours in the morning drinking under the sakura tree.

Osaka to Hiroshima Bomb Museum?
You have to take the first shinkansen out of Osaka which is 6AM to make it in Hiroshima around 8 AM.

good advice. some days are pretty full but there are some relaxed ones too - and there is the evenings to relax over dinner and a few drinks. The night at the ryokan in the middle of the trip should be great.

thanks to samurai and samokan for the idea's for sakura viewing!

my only other question really is about weather and if jeans, tee, light hoodie and a leather jkt will be good???

That should be fine.

yeah basically it would be sufficient, but sometimes it at night temperature (sometimes) usually drops a bit..