Just starting to plan a 3 week journey to Scotland. A couple looking to rent a car and go, sometime around May. Open to suggestions

Suggestions for <i>what</i>?

That is an entire country --

You chose Scotland for some reason(s) so give us some help here.

As it stands, this is an impossible question to answer. I think you need to do some work first. Get a decent guide book - Eyewitness Scotland is a good one. Alternatively have a look at the different itineraries on this website which will give you some idea of what you can do.
https://www.secret-scotland.com/

<i>Open to suggestions</i>

-Drink whisky
-Eat haggis
-Go to a ceilidh
-Buy a kilt
-Eat a deep fried Mars bar
-Take the Loch Ness boat tour
-Get locked in a pub and stagger back to your bed at 3AM
-Get into fisticuffs with a local in a pub
-Go for a ramble and get eaten by midges
-Go on distillery tours
-Go to a shortbread factory
-Eat black pudding with your breakfast
-Eat kippers for breakfast
-Walk around Edinburgh castle
-Go shopping on the Royal Mile

You forgot the fruit pudding and tablet from your list. Remember you have to first catch your haggis...

Suggestions:

-read some trip reports and planning threads about other people's driving trips of Scotland, here and over on TripAdvisor

-go get a huge pile of guidebooks on Scotland, read up, and decide what you want to see (books are free from the local public library, and the helpful staff will find you many more than you knew existed, or you can buy them)

-make a list of what you want to see and do and use that, plus a map, to start to plan your itinerary

Best of luck with your travel planning!

Bit of a Slacker here. Thank You for the feedback.
So my very rough draft

Day 1. fly into Edinburgh, rent car, check into hotel ? on Royal Mile, explore,
Day 2. Explore Edinburgh, Castle, Arthurs Seat, Palace, Overnight
Day 3. Depart early towards Glencoe, stopping at Doune Castle, Inchmahome Priory, Overnight Clachaig (booked)
Day 4. Explore Glencoe, Overnight Clachaig (booked)
Day 5.Drive to Mallaig take Ferry to Knoydart, Overnight
Day 6. Explore Knoydart, some hill walking, Overnight
Day 7. Ferry back to Mallaig, Take Ferry to Isle of Skye, Overnight
Day 8,9. explore Isle of Skye, Lighthouse, Talisker Distillery, Fairy Pools, Donvegan Castle, Overnight
Day 10. Drive over the Skye Bridge head to ullapool, Overnight
Day 11. Explore Ullapool Corrieshalloch Gorge, Knockan Crag, Overnight
Day 12. Drive to Durness, Overnight
Day 13. Explore Durness, Smoo Cave, Beaches
Day 14. Drive to Ferry to Orkney, Overnight
Day 15. Explore Orkney Pre-Historic Sites
Day 16. Ferry off, Drive to Wick and Overnight
Day 17. Drive to Inverness, explore and Overnight
Day 18. Explore Inverness, Loch Ness, Culloden,Overnight
Day 19. Drive to Ballater, Overnight
Day 20. Explore The Cairngorms National Park
Day 21. Drive to St Andrews and Overnight
Day 22. Drive to Glasgow and overnight
Day 23. Glasgow?
Day 24. Drive to Edinburgh and Overnight
Day 25 Fly Out
I'm not to sure about the last week. After Inverness should I Head back to Oban and back to Edinburgh in that direction?
Should I add another isle?. I'm locked into hotel in Glencoe and waiting to here back on B &B in Knoydart. Thanks again for your input

slacker has what appears to be a well-thought out plan but I would not rent the car until ready to leave Edinburgh and return it bu driving from Glasgow to the airport to return it there. Put a day or two into Edinburgh at beginning of trip sans car - save a few days of car rental in a city where cars are useless.

You will have absolutely no need for a car in Edinburgh and few places on the Royal Mile provide parking. Pick up your car at EDI the morning of day 3.

You have some long days but not terrible. Day 20 doesn't really make sense. You will be on Deeside and in the middle of the 'Castle Trail', so I'd use my time there instead if back tracking to the NP.

You will have next to no time in Fife . . . I'd drop Glasgow and add those two days one each to Ballater and St Andrews.

Thank You for the feedback.
Is it really that easy getting to and from the airport? I understand that we will not need the car, but We will only be in Edinburgh for 2 days. I thought it would be easy to just have it done.

Could not be easier getting to the airport . . . Taxi, Airbus, or the tram. Tram is the cheapest and very easy, but if the weather is nasty or you have a lot (too much) luggage you'd probably want a taxi down to Princes street to catch the tram.

The Airlink bus leaves from Waverly Bridge and is an easy (meaning down hill) walk from the Royal Mile.

Edinburgh is an OLD city (esp. Old Town) with narrow thoroughfares and twisty streets and barely drive-able before they put in the light rail lines.

Inverness is not really a tourist destination in itself, it's a gateway for what's nearby: Culloden, Cawdor, Dunrobin, Nessie's swimming pool, etc.

Unlike Janis, I don't recall any hills in Edinburgh that actually go down.

BigRuss . . . The only reliably down hill walk is to Waverly Bridge

But that is ONLY from the top end of the Royal Mile (from or just below St Giles) . . . Otherwise yep, you first need to walk up hill on the RM before you can go down hill to the bus stop.

You can also pick up a car at the Waverly train station.

. . . But that requires driving through central Edinburgh which isn't easy at the best of times, and utterly horrible at the worst of times.

Much much easier to collect a car at EDI.

Good thoughts, thank you. I have booked a B & B in Edinburgh that has a parking spot. So now the car will not be a problem.
I also had to change some days around. Not to my liking but its done. So
Day 5-7. Glencoe to Isle of Skye, for 3 nights in Portree B&B
Day 8&9. Then drive and ferry to Knoydart for 2 nights B&B.
Day 10. Should we still drive to Ullapool? I have not booked anything past day 9. So that is still open for suggestions please