Have stock chart update stock and clear itself

My Boss just came to me and asked me to start a spreadsheet to keep track of parts. well parts are going in and out of the cage at all times so instead of creating a LOG to keep track. I wanted to make a part list then create a seperate section so someone can put part x. took out or added y amount. and the sheet will just update itself.

more details.

[A1] / [A2]
drop down menu for everything in list below D1 (already know how to do this) / QTY Added or subtracted

[D1] / [D2] / [D3] / [D4]
item / Description / QTY / Last Updated
Case / server / 15 / would need to record time and date of this action

So when someone opens the spreadsheet they just select case from the drop down list in [A1] and enter -5 into [A2] and as they hit enter [D3] will change to 10 and then [A2] will clear itself so the next person can put in there changes. plus [D4] would record the date and time this change was made.

also... if possible I would like sheet 2 to keep track of all the changes. if possible. if not this is not a big deal. would just be nice. (side note. I would want this one to keep track of who was logged in and what time when the changes where made.

after this is done. my boss would like this uploaded to Google Sheets if its possible.