Replacing the screen - questions

Nowadays I own a Galaxy S6, I remembered my old pal the nexus 4 which has been sitting in my drawer for quite sometime, I thought " I want to get this fixed" so I did some research and ordered some parts. My nexus 4 began having erratic touch problems and ended in the lower half of the screen to be completely disabled, I basically can not use the lower part of the screen .
These are the parts I ordered :

1- http://www.amazon.com/gp/product/B00...ilpage_o03_s00
LCD Touch Screen Digitizer Assembly + Front Frame for LG E960 Google Nexus 4

Since the nexus 4 has has the digitizer coupled with the LCD, its hard to separate them and I really do not want to take the time.

2- http://www.amazon.com/gp/product/B00...ilpage_o00_s00
Leegoal (TM) T5 T6 Philips Slotted Screwdriver Opening Tool Set for Cell Phone

I know that the screen comes with tools but a lot have reported that some do not work properly.

3- http://www.amazon.com/gp/product/B00...ilpage_o01_s00
Pre-cut Double-Side Adhesive Tape Strip Sticker for Google Nexus Touch Screen Digitizer (for LG Google Nexus 4 E960)

As it states, it’s for the Touchscreen to put on the frame.

After I have explained everything, I can start my questions,

First, I have seen many guides and they remove the battery and the motherboard and speaker, to put the display , why is that ? It can be connected by just disconnecting the old display, is it because of the heating to remove old display ? why not just disconnect the battery ?

second, is that I want to use the old frame and not take the time to transfer everything to the new frame, which might damage something, but the battery adhesive has to be reapplied or not ? It seems like the battery fits in place without it.

Third and last, Is it okay to use any double sided tape under the battery or is it some special tape?

I hope I did not bore you, can anyone please clarify the points above?