I keep paper and electronic. I do one entry per day and in the remarks I put in all the legs I flew that day. I took my paper logbooks to my interview. The electronic logbook is a huge help when it comes to filling out the applications.

If you get the interview with a major and have a neat, hand written logbook(s), that will not be the reason you don't get the job.

I use LogBook Pro and entered all the data myself.
I checked the electronic data against the analog (written) data and made corrections on each page as needed.
Took me a year doing one or two pages a night but sure makes it nice if you need to break down the data.

I suggest double checking each page for errors.
Remember, garbage in=garbage out.

I was in the same boat as you are, I had roughly 8100 hours to log. I bought Logbook Pro and got to work, starting with my first discovery flight 18 years ago. It took me a couple of months of plucking away at it, but I did leg by leg and it was a pain in the ass. When I was all done I brought the electronic file to the FedEx store and had it printed. It was worth the time and money and most importantly, Delta seemed to like it...:-)

What do you do about endorsements and sign-offs etc

LogbookPro offers that service

What kind of endorsements and sign offs do you need at this point? Keep them in your paper logbook. Logten pro I think lets someone sign it with their finger for that purpose. Could always annotate it in remarks and put their cfi# in or something. But I don't think Delta is going to ask to see your complex endorsement. Anyone in the 121 world should be beyond needing endorsements. Not like an airline signs your logbook endorsing you to take a checkride or signs it after your checkride. Could also print out a page to get signed and scan it and attach it to the digital logbook. If you are flying GA and get ramp checked the Feds don't ask to see your endorsements to see if you are legal to fly a plane.

Frontier wants to see all your endorsements in the interview. From the interview email-

We will also need to review all of your original logbooks and endorsements. If not, you will need to produce copies of your company/ flight school signoffs, endorsements, and FAA documents detailed in Advisory Circular 120-68F (including 8060-5, 8060-72 and 8710-1) at the interview.

I scanned them from my original paper logbooks and made a digital copy and put them in the back, along with all the other pretty graphs and breakdowns that Logbook Pro offers. Also, I did the electronic signature and imported that onto every page.

I recently joined the electronic logbook world too and yes, went line-by-line, not nearly as much flight time as those guys but man alive, once you get caught up, it's so worth it moving forward.