Samsung Galaxy S4 — SGS4 - Intermittent Pause - Limited Memory Available - Factory Reset? - Root?

My AT&T SGS4 is showing its age. Yet, the phone basically meets my needs and if I can eliminate the problems I would be happy to use it for some time to come.

First problem is my 16GB memory often hovers at 500MB or less. The phone does not operate well, app wise, at that level. A few minutes using the native memory manager functions followed by using DU app boosters and functionality gets better, although apparent available memory does not increase markedly. All apps that can be moved to the SD card (16GB) have been moved. and over time and use the problems return.

Second problem is I have an intermittent pause. E.G. - i am creating a text or email, suddenly there is no actvity on the screen, but then a series of already executed key strokes appear sequentially on the screen. I think I have seen at least 4 so appear. This fault also stops the music player and the web browser. On the music player it is a dead stop and has to be reactivated.

I am thinking these problems require, or can be solved by, a factory reset and then, possibly, rooting the phone to rid the unit of the bloatware.

First question, what happens during a factory reset, is the phone tied up for hours as it sequentially updates OS' recapitulating each OS version it has had previously? Currently I am 4.4.4. An OTA update to Lollipop failed due to the memory issues. I do not know what OS I started with.

Second question, if I root, must I install a custom ROM to be able to rid the phone of bloatware. I am technical enough to be dangerous, and would best be described as a user who knows what an OTA and bloatware are but can quickly get confused by hardcore tech speak.

Finally,beyond my specific questions any insights that can be provided by the community will be gratefully received.

Thanks