User form calc, passing variables,cmb box issue

-Have user form with sceenshot included here. I need the cmb to look better. i only have 4 values in list. do i just use properties and resize etc..or is there a way to always show top value in list?
- I need the focus to move to next text box(volume bbls)- BUT users can choose the same tank so the value of txttank may not change. How do i ensure no matter what value they choose, the tab will move to volume after entry of tank #.
- i need a simple calculation on exit of txtMON. do i use EVENT, like key up or down, or soemthignto that effect. I dont want to use the cmd button i have temporarily placed. its simple addition and then dividison so its unneeded. simplest way upon exit MON value, for the next field (txtrm) to autofill with answer.
-i have reviewed syntax help on excel vba, but i really need to know a few things..like meaning of what options i have avaialbe...when i use the syntax help, eg. VALUE...i dont see real life examples..i guess i need a good code basic manual with the 'notes" or "code explained" in green in an example...they tend to have one line or many lines, and i need to know what like does what? does anyone have a suggested site or reference location? my brain gets tired of fighting with this..

Thanks ahead of time for any help you can give.