3 Hrs form Edinburgh....
On the east coast that could potentially take you as far as Aberdeen, I'll leave the east coast bods to expand on that one,
Heading west, You could probably get to Oban in 3 hrs, & if you want total seclusion, Chuck the boat in at Dunstaffnage and after a fight with the Connel narrows you have a good few miles of Loch Etive which basically ends up in the middle of nowhere. If you are thinking 2 days, that might be a bit limiting? You could also launch at the Taynuilt pier if the tides were bad for the Falls. If you launched at Dunstaffnage-ish, heading up Linnhe gives you plenty of places to go & explore, in relative shelter and there's a garage about 1/2 a mile round from the Ballahuilish bridge which is a short scramble up the bank to fill your tank(s). You then also have the choice of camping somewhere or plenty of places with pubs! I've done a chunk or two of there in an 11' Dory
, so it's not "Redbay only" territory
- but do keep an eye on the wind direction, as a "straight up the loch" wind will make it a bit more interesting.
Alternatively there's the option of a lap of Mull & / or round Ardnamurchan or head south to Sween / Jura / Islay (or a combination thereof) but I'll leave the locals to big up that area!
Largs is easily doable in 3 hrs (ha, says he remembering the M80 roadworks now have the "Yellow vultures" installed) - from there it's a relatively short hop to Loch Fyne - the Eastern shore of which probably ticks the "out the way" boxes, but also allows you relatively easy access to the A83 on the western shore should it all go t!ts up.
Alternatively doing the inverse of Doug's suggestion - why not launch at the top of Loch Long & work south from there......