If you don't want to pack walking poles then you can find them once you get to Scotland. There are plenty of outdoor shops in Inverness, e.g. Tiso (fairly upmarket) is a bit like REI, or there's Go Outdoors (budget), Mountain Warehouse (budget), Cotswold Outdoor or Trespass.
You will need to take account of the wind and rain, which can occur year round! Layers and a windproof, waterproof outer layer are key. You will need hiking boots too. I wear either a wind and waterproof jacket or a down jacket year round depending on whether it looks like rain when I head out. Whichever jacket I'm not wearing will be in the car as the weather changes fast.
How close to Inverness are you staying? It's a good 3 hours from Inverness to where I live in North West Skye. Plenty of decent hiking closer to Inverness. Have you checked out Walk Highlands for options?