In addition to the previous post a new trail has been created that will allow you to walk around the Loch - it's called the Loch Ness 360 and it's a great option if you want a multi day trip around the Loch.
It's all on good quality trails with the most significant ascent being between Invermoriston and Drumnadrochit and then between Drumnadrochit and Inverness.
The elevation profiles are at the bottom of the page here: https://lochness-360.com/
It's not a big mountain area around Loch Ness although the geology does mean that it's steep sided so the paths near the loch do tend to be up and away from it. Your high points are hills like Meall Fuar-mhonaidh but these can be easily avoided if you don't fancy tackling higher ground.
If you're basing yourself out of Inverness every day then you might want to consider a variety of day trips.
It's impossible to walk around the loch in a day (unless you run it!) so a variety of different trips might work.
Options could include:
A day climbing Meall Fuar-mhonaidh at Drumnadrochit. You'll get great views down the loch from there - it's a boggy walk though, so take good boots.
Explore the South Side Loch Ness - Dores and the Falls of Foyers are a good way to spend the day.
Fort Augustus could be an easy day checking out the lock gates on the Caledonian Canal and mooching around the shops.
Another day in Drumnadrochit - Loch Ness Exhibition Centre, there are boat trips on to the Loch from there and there's a few walks you can do that give great views of the loch - suggestions in my own signature 🙂.
Of course Urquhart Castle is always worth a visit too.
There's a variety of boat trips on the loch, including speedboats if you fancy a little more excitement!
Hope that helps!