Some say you MUST go on a tour which allows you to "skip the line"
I depends on what you mean by "MUST" and by "a tour". You cannot just walk around in the castle by yourself; if you want to see the inside, you MUST go in with a "tour" by one of the castle's guides and stay with the group. But that tour is just from the front door of the castle to the gift shop just before the exit.
There are also third party tours that take you out to the castle by public transportation or by charter bus, and charge you a pretty penny for the service. You don't have to take one of these tours, and, IMO, they are a waste of money. The advertised price of these tours does not include the price of the guide tour of the castle, but the guide does take your money and gets the tickets for you (hardly worth $50). You do get to skip the line (the line of people who show up at the ticket kiosk without reservations), but if you have reservations you collect your tickets at a much shorter line. The last time I was there, there was no one ahead of me in the ticket pickup line. The third party tour does not take you up to the castle - you walk, or take a horse carriage - but with 1½ hrs from ticket pickup to tour time, that's not a problem. I remember it being a walk of about a half hour, maybe a little more. There are restaurants by the ticket kiosks in Hohenschwangau, and if you don't want to walk up the hill with a full stomach, there is a restaurant about 2/10th mile from the castle.
If you make reservations in advance, make them for about 2:30 pm (14:30); that gives you a half hour (which you won't need) at the ticket kiosk to pick up you reserved tickets. Leave Munich just before 10:00 with a Bayern-Ticket (25€ for 1 person, 31€ for 2), arrive in Füssen at 11:55 and take the bus to Hohenschwangau from the bus stop in front of the station. It leaves at 12:05 and gets to Hohenschwangau at 12:13. The bus is included with the Bayern-Ticket. It's a short walk up the hill to the ticket kiosk - it shouldn't take you 17 minutes.
With a Bayern-Ticket, you can't start using the ticket before 9 AM, but if you go on a weekend day, there is no limit to when you can start If you purchase an MVV inner zone ticket for 2,90€/P, you can use it for the train connection as far as Pasing where you leave after 9, and use the Bayern-Ticket from there. In that case move all the times up an hour (e.g., make the reservation for 1:30 PM.
If you drive to the castle from Munich, it will take about 2 hours, but provide plenty of extra time when you make your reservation to account for traffic jams, getting lost, etc.