Hey Andrea
Welcome to the forum, and June is a brilliant month to go. The weather in Scotland is always unpredictable, but for sure you'll have lots of daylight: just as well, since you'll have to average 19 miles a day

For a 5-day walk, I'd suggest overnighting at Balmaha, Inverarnan, Bridge of Orchy and Kinlochleven, which would give you days of 20, 21, 19, 21 and 14 miles respectively.
You don't say anything about your budget or experience, but if you are more specific we can try to help further. Good luck!