My 2 cents - depending on the company and the way their talent acquisition works, it might be a combination of the recruiter responsible for the role you are applying for is overworked, demotivated, working out notice(!), or has been on holiday over xmas and new year and still trying to catch up with emails etc.
It might also be the hiring manager has been on hols, hence the delay. If the role is currently vacant the existing team are probably in over their heads.
That being said, this experience is probably a taste of things to come after you join, so bear that in mind.
On the compensation side of things, do you have a realistic number in mind below which you wouldnt consider the role? If so it's worth being realistic on this and just walk away if they cant offer it. I assume you have knowledge of the labour market in what you do so you would know what is reasonable or not. You can also ask for details of employee benefits which should be standardised in any case. In a big company these things are typically included in a job/role acquisition so they should have that information.
Do you have job description now? it's worth asking for one in any case.
More widely, agree that interview practice is always good. Whether that is worth 1/2 day of annual leave on your part is your call. Most companies, especially the big ones, I know would accommodate at least the first interviews with HR etc after 6pm. If they dont, again it's worth asking whether this is the kind of corporate culture you would like. Some would, some wouldnt. Again your personal choice!
Anyways my 2 cents. Good luck with the application and ongoing job hunt in any case!