I would recommend to directly reply to the email from HR, thanking them for the information. Then mention that you would like to clarify on logistics. Since you arrive from XYZ, should you go ahead and book the travel, or will this be supported by them. There is no problem in asking this question - especially for Tier 1 firms.
I agree with previous replies - simply ask in a polite way.
What you should not do by any mean is to arrange your own travel and accommodation and try to bill them afterwards without asking priory - this might seem silly but have seen it in the past, so avoid it
This is simple, just ask their HR
there are no problems in contacting HR asking for such information; Tier 1 companies always pay for travel expenses for interviews so will inform you accordingly.