Sam both this question and your question about cash or credit cards have been answered many times on this forum. Just do a little research.Edited: 10 June 2018, 05:33
Easy to get a visa on arrival and no problem about your return ticket.
30-day Lao VOA easy, bring a passport-size photo and best paid in USD ($35 for UK nationals). Onward flight not an issue. Obtain local currency (Kip) via exchange or ATM but spend or change back before leaving (common mistake).