Uni admin is cut to the bone due to funding cuts and academic staff can be a bit entitled but they are a minority. Expect to work hard and be aware that uni's are having to adopt more and more flexible approaches to students' needs and student services are often now expected to be on rotas covering a 9am to 7pm pattern.
Overall, however, there shoukd be more opportunities for promotion than in a school. If you are within the M25 the London uni's find it hard to recruit due to higher pay and competition from central London. Jobs there are usually quite plentiful. In other parts of the country university admin jobs are closer to gold dust as the the universities are regarded as Employers of Choice.
Annual leave on the lower grades is usually 25 days, plus Bank Holidays plus a Christmas closure of about a week or more. Some also offer a couple of extra days at Easter. On higher grades a/l increases up to 35 days.
Benefits are: annual increments to top of scale, annual cost of living awards (often stingy), good pensions, generous A/L as aforementioned, generous sick pay and a brilliant pension although this is likely to be watered down in the next 3 to 5 years due to the valuations and employer costs.
Read the person spec carefully and address all items on the application form. Think carefully about scenarios you will be asked to answer which are likely to be around: prioritisation, volume management, dealing with a difficult or demanding team member or academic, etc. Focus on using outlook reminders and daily spreadsheets rather than sticky notes on your desk! They may also throw in a safeguarding question such as what would you do if a student told you in absolute confidence they were suicidal. You would tell them that due to the gravity of the disclosure you had to report what they had told you and refer it to your line manager or a named safeguarding lead.
There's also likely to be an in-tray test to check your basic literacy and numeracy so make sure you can convert a fraction to a percentage and work out both and mug up on your excel skills - simple data manipulation shoukd do it and make sure you can add up columns.
Good luck!