[Specific places for items]

You might find this page useful

https://www.imperialofficer.com/forum/index.php?/topic/1817-IOC-Costume-Resource-List

[Merr sonn power 5 blaster]

I got one from Q's Prop Shop.  He's on these forums.  They have lights, sound, and are really, really awesome.  I'd recommend.

+1 on this.

[Making one costume work for tie pilot, bridge crew and tie reserve]

Hahaha

[Making one costume work for tie pilot, bridge crew and tie reserve]

This is awesome!

I noticed there is also an Imperial Navy Trooper variant that contains the dress uniform, not sure if you knew about that one.

https://databank.501st.com/databank/Costuming:IN_imperial_navy_officer

I recently completed the following matrix to more clearly show what components are required with each variation.  Hope this helps!
 
imgur.com/hxppuwp.jpg