2 week trip itinerary...all feedback welcome!

You may be underestimating the distances from city to city on your trip, and your itinerary will probably result in your trip being one big blur. Your first and last day of any European trip will be wasted days. And every time you have to move from city to city, you're also losing a day.
I would suggest you limit your trip to a couple of days in Scotland and take a budget air carrier down to London for a 5 day minimum. Then take the Eurostar down to Paris for the remainder of your time.

And if you're looking for a $500 flight each way in June, you're probably not going to find it out of Seattle or Vancouver.

It seems like you need another week! Seriously, it is too much for two weeks. Mentioning the airfare and hostel stays says you are watching the budget closely, yet you are adding a lot of expense to travel to Germany for so few days. In turn, you are not giving enough time to the locations in the U.K. Going to Glasgow for a free bed and not having time to see or do anything? Edinburgh (note spelling) is certainly worth more than a one night stay.

I suggest you drop Germany and the expensive car rental. That gives you 5 nights to add in elsewhere. Stay in Glasgow another night and add a night ech to Edinburgh and London, and 2 to Paris. Fly home from Paris.

Conventional wisdom, for what it is worth, is to buy international fares 90-120 days before travel. I would start strategizing and searching the 331 days out the airlines post schedules. Certainly look at WOW Air for travel through Iceland, although that might add a day to your travel. Can you land in Glasgow or will you be forced into London with a connecting flight or train? Sometimes going for the cheapest fare adds to expense and travel time. Be sure to calculate in transfers to get to your starting point.

Wow! A month's itinerary squashed into 2 weeks! I agree with the previous posters, cut Germany. Fly open jaw out of Paris.

I don't know about booking airline tickets on your side of the pond, but here, we often book as soon as tickets become available. I would never leave transatlantic flights to only 90 days out! Prices only go one way. Prices here to America are rarely under £500, so I am amazed that you can get them for $500.

Add at least another night to Glasgow and Edinburgh. You should visit the former royal yacht Britannia and take afternoon tea onboard. Book your rail tickets to London 12 weeks out for the best prices. Travelling after 9.30, as you are planning, will be cheaper.

London accommodation - look at YMCA but also check out Premier Inn and Travelodge, which are value chains and the best prices are again booked months before travel. If you're travelling in peak season, also look at LSE as they let out their student rooms in the summer holidays.

Take the Eurostar to Paris and I think tickets are available 6 months out. Prices increase and don't drop for this service, so don't hope for a last minute bargain. Travelling outside peak periods will be cheaper and avoid Friday night, Sunday night and early Monday morning journeys as these are busy with commuters and weekenders.

You abbreviated UCA Farnham. I don't recognise it. What is it when spelled out? The reason I ask for what the travel time would be to St Pancras station in London for the trip to Paris, or depending on where UCA Farnham is, maybe a cheap flight.

As for the rest of the trip, you really are trying to fit a gallon in a pint pot.

Take a look at Condor Air. They fly form Seattle to Glasgow via Las Vegas and Manchester. Makes for a long flight but very inexpensive. You cannot reserve for June 2017 yet, but you can explore. It seems they do open jaw, too, and serve Paris.