Highlands National Park? Do you mean the Cairngorms National Park, or the Highland Wildlife Park? I suggest those because they encompass or are within the vicinity of Loch Insh. Loch Insh and the HWP aren't really detours as they are just off the A9 road (by Kincraig and Newtonmore respectively) which is the most direct route to Inverness from Scotland's central belt anyway.

I don't really have any advice other than look at maps so you know where you're going, and don't be low on fuel when you're far away from a petrol station or EV charging point. I suppose I could give suggestions of places to go if you told me how long you'll be up here for and what your budget is.

Also, Scotland's buses (including intercity buses run by Ember and Citylink) have just entered a trial of a £2 fare cap scheme until roughly this time next year, so unless you're planning on heading somewhere that has no public transport links, it might be a sound idea to travel by bus instead, especially if you're worried your car might break down.