As for the train, you literally need to book weeks ahead. Almost as bad as trying to get a points ticket on SQ. These days I drive…though I have ‘discovered’ that Canberra is an easier drive and has shopping that’s just as good.
The Sydney-Melbourne XPT trains that serve Albury and Wagga Wagga can be unreliable - on some recent hot days (such as 43-45 degrees forecast at Wagga Wagga/Junee), road coaches have operated in lieu, or occasionally the train from Sydney terminates in Albury if very late due to heat speed restrictions or other reasons. Today the Sydney-bound XPT was 25 minutes late near Yass Junction while the Melbourne-bound day train was nine minutes late at Chiltern.
However even in school holidays and at other peaks such as pre-Easter there should often be NSW TrainLink tickets (and hence seats, as XPTs are compulsory reservation) south of Wagga Wagga in each direction, as more passengers tend to travel Albury/Wagga Wagga/Cootamundra to/from Sydney than from Melbourne. I include 'Cootamundra' as the daytime XPTs have many connecting road coaches at that hub.
NSW TrainLink XPT fares are much higher than V/Line's.
V/Line's single (i.e. one way) adult fare is $11.40 Southern Cross to Albury. Concession fares (seniors, pensioners etc.) $5.70. From 1 January 2026, youths/children under 18 travel free (but must have a paper ticket, or Myki Youth Pass if only travelling Melbourne-Seymour-Melbourne), and seniors on weekends were already free.
Demand for V/Line travel on the Albury line has become huge, given Albury/Wodonga alone has a population of 100,000. The shambolic Victorian state government has therefore introduced permanent compulsory reservations (exception: Seymour to Southern Cross or vice versa that's within the myki zone, but you may have to stand for the whole journey). No other V/Line long distance route has compulsory reservations.
I doubt all V/Line trains are booked out 'weeks ahead': the late afternoon departure from Albury and the early morning one from Melbourne are less popular than the other two daily frequencies in each direction.
V/Line also operates two weekday return Seymour to Albury road coaches (one return trip on weekends) that connect at Seymour from/to Southern Cross: slower than the through trains, but has the advantage of being completely unreserved. (I don't know what occurs if more passengers turn up than the coach will accommodate. In the past, V/Line then tries to source extra coach(es) but that means a delay).
The route 901 bus from Broadmeadows to Melbourne Airport offers a good 15 minute frequency on weekdays until c.2100 hours, then half hourly: latter is the frequency on weekends and public holidays. I have never experienced any trouble from youths at Broadmeadows but it doesn't have the best reputation.
@serfty seems to often use it.