A couple of days spent in Glasgow would be more than enough to capture the local architecture and some of the museums and other a attractions. If you like pubs then you’ll be at home here and the restaurant scene is booming so you’ll be spoilt for choice. The good news is that Loch Lomond and/or Loch Katrine is an easy day out from Glasgow and there’s a great distillery (Glengoyne) less than 40 minutes from the city and a number of operators run minibus tours to here. At the end of your trip I suggest you give yourself a little more time in Edinburgh, there’s so much to see and do - and all easily walkable, so no need to worry about transport.
As other posters have commented on when the question gets asked, beyond Scotland’s so-called Central Belt (which links Glasgow and Edinburgh), direct trains will get you to most of the other bigger cities and towns but this will leave you in most instances in the city/town centres from where you need to pick up local buses or even taxis to get out and about to explore the surrounding countryside. All doable but needs extra planning.
Try getting in touch with www.culturalperspectives.co.uk. They’re new and based in Glasgow I believe and specialise in small group, bespoke tours, mainly art and architecture which might not be your thing (too niche?) but I know they’ve taken folk from Glasgow and up through Glencoe and out to the islands of Mull and Iona.
Closer to Glasgow, the Isle of Arran is also feasible (direct train from Glasgow to Ardrossan, then 1hr CalMac ferry to Brodick). Not sure of local buses once on Arran which might limit your freedom but they have a brewery and distillery amongst the local attractions. That said, unless you’re planning some serious all day trekking (Goat Fell?) you’ll find enjoyable walks I’m sure, or you can hire bikes. There’s just one significant road that runs round the whole island and even here there’s often barely room for two cars to pass so no need to worry about traffic. As with most parts of rural Scotland dealing with traffic is rarely a problem; coming face to face with sheep blocking single-track roads can sometimes be an altogether different problem but it’s all part of the fun so Enjoy.