4s replaced by vendor at ios7, my backup was 7.1.2 - go to 8.1? best steps help? (FIR

[cwinte]

So I have 4s with working wifi thanks to my ebay supplier swapping out a wifi failure. But I had my old 4s at 7.1.2 with 150 apps and loads of settings - I'd like to get all that back.
So before sending for replace/repair I backed up over cable to iTunes.
New unit arrives back 10 days later (post...) ios 7.0

Waited a bit to see if 8.1 sounds good idea, maybe yes (agree?)

So what are the steps to get a good restore and update done.
Ideally I'd like to keep recent texts received since the "new" unit arrived and merge with previous texts, but maybe I have to choose old or current?
Or is it old only?
I am up for a bit of extraction from the backup files on my Mac if needs be, crank up terminal again...

I guess same applies to call log though not too worried to end up with old on that.

>FIRST POST< so...
HI, thanks in advance for the guidance which is to come (hoping)

 

[cwinte]

a bit more info (no iCloud backup etc)

Should have said that I do not use iCloud syncing or backup...

Can I just apply 8.1 update and then do a restore of my 7.1.2 backup?
Does that give me 8.1 with 7.1.2 apps, settings, data or what?

What happens about texts (old messages in backup and new messages received since I got the replacement phone back)?
To get these iterrim texts am I best to make another backup of this phone right before applying 8.1?