SCOTLAND inverness to fort william to cairngorm on loop

Inverness to Fort William can be done on the Great glen Way, which Ive cycled sections. This section(Inverness to Fort William) could easily be done in 2 days, but is possible in one according to a friend who has done it.
Fort William to Crainlarich can be done also but is pretty tough in sections, I dont know of a realistic timescale as ive only been on small sections on the bike.
I havent been to the tay forest park area with a bike, so im unsure where to go there etc
Going back north through perthshire to the cairngorms to inverness would be the national cycle network which roughly follows the A9, (Tay forest to Aviemore area is about 50ish miles) and will take you to the trails near aviemore, and can take you through the"Burma Road" north to Inverness.
Aviemore to Inverness is about 30 miles.
Near Inverness there is Learnie Red Rock trails on the Black Isle near Rosemarkie, The Strathpuffer route at Strathpeffer near Dingwall and Abreachan trails near the north of Loch Ness.
Ben Nevis is, apparantly cyclable but as far as i know you'll have to push up, and watch for the lots of walkers on the decent! It is ok to take a bike up Ben nevis, but may be frowned upon. Due to the location of Ben Nevis paths I dont know if it would be cyclable directly on to the red route xc(I take it that s the one you mean?) You can push up if you dont want to pay for the Gondola tho!!!

Andrew has pretty much got it covered but here's a few other thoughts that spring to mind. And apologies in advance for the long post !

Inverness to Fort Bill - you could go down the Great Glen way as far as Fort Augustus and then turn to go over the Corrieyairack Pass. This would bring you out right at Laggan Wolftrax. There are a few bunkhouses nearby where you could stop for the night here I believe.
Downside to this idea is that it leaves you with little choice but to head to Fort Bill along the A86 until you get to Roy Bridge before you can start to pick up any off road options again. You could do Corrieyairack again though !

Another thought on the Inverness - Fort Bill route would be to stay on the Great Glen way until you get to Invergarry, where you can turn right towards Wester Mandally and follow the forest road to where it crosses the Allt Ladaidh burn at NH23010028. From here turn south until the road runs out, and follow the path that turns south west around the back of the hills called Meall a Choire Ghlais & Sron a Choire Ghairbh. Turn left and climb your way up the path beside the Allt Cam Bhealaich ( this bit is tough ! ) until you reach the top of the pass, and try to contain yourself as you look at the singletrack downhill you've got yourself down Cam Bhealach. It is brilliant. This comes out onto the Great Glen way about 7 miles south of where you left it at Invergarry.

You mention Ben Nevis, but I'm a bit unsure what you mean about the top of the Nevis range. You can get a bike to the top of Ben Nevis up the tourist route from Glen Nevis, but it'll take a good bit of pushing. Are you asking if you could then get from here to the top of the Red / World Cup downhill routes to save you the price of the uplift ?
Well.......you could but you'd be carrying your bike. There's another mountain in the way first ( Carn Mor Dearg ) and then you still end up on the wrong side of Aonach Mor from the downhill routes. Way too much effort !

If you're wanting to do the Red / WC routes take the gondola. If you don't want to pay then I'd not bother with pushing my way up from the gondola start point either- just do the Witches Trail xc route instead, it's free and it's fun.

When you're heading north back up the A9 corridor to Inverness, another option for you would be to go through Gaick Pass rather than follow the railway and A9 through the Drumochter pass. It'll get you into the wilderness for a few miles and it's pretty easy going, and brings you back out at Kingussie. At this point you're only a few miles away from Laggan Wolftrax which might be your best option for picking up Laggan on your trip if you haven't done so already at this point.

I go to Learnie Red Rock frequently and enjoy it. If you're cycling there from Inverness though it's probably worth pointing out that it's at Rosemarkie as Andrew has mentioned, some 18 miles or so ( by road ) north of Inverness itself.

Scenery wise the Great Glen Way is excellent. Occasionally it climbs it's way up the side of the hills to give you fine views up and down the glen.
Can say the same for the West Highland Way, in fact I think it's better, especially the section from Fort Bill to Tyndrum. I'm not sure exactly where Tay Forest Park is but I'd imagine you'd be on the WHW until Tyndrum before heading east ?
You shouldn't have too much problem free camping. I've never done it myself, but I've seen tents in the wilderness often enough to suggest that there are plenty folks who do.

You can cycle to the base of the gondola route at Fort Bill no problem. There's a cycle path from the centre of the Fort to Aonach Mor base station. The Witches Trails start from here so no need to spend any cash getting onto the hill. You only need to take the gondola if you want to do the Downhill or Red Routes.

Corrieyairack is good cross country, a little tough in places, but you are climbing a considerable height, and again with great scenery. Never done it with a tent on my back though !

How best to spend 7 days touring ? A tough one. Ask 10 folk and you'll get 10 different replies, all of them good ideas.

My starter for 10 would be ;
Inverness to Fort Augustus on the Great Glen Way.
Over Corrieyairack to Laggan and a visit to Wolftrax.
From Laggan to Spean Bridge along the A86, then onto the A82 towards Fort Bill for about 1km to Aonachan. Turn south into Leanachan Forest and follow this cycle trail to Aonach Mor and Fort Bill for a day or two.
WHW from Fort Bill to Tyndrum, with a visit to Glencoe on the way past ? ( Need to pay for the lift though, and it's not ideal for an xc bike ! ).

Depending on your fitness level you could do this in 4 days, or make it last you a week if you spend a day at Laggan and Aonach Mor. Once you get to Tyndrum you're getting beyond my area of knowledge, until you get back onto the A9 corridor between Perth and Inverness again.
As mentioned previously in other replies, there's loads to do at Aviemore as well. Just difficult to get it all in !

I don't know too much about Boardman bikes - is the Pro a hardtail or full susser ? Either way I'd imagine it'll cope, as I've done the Great Glen, WHW, Wolftrax and Aonach Mor Witches Trails with a mate who rides a Genesis Core 10 and it's survived to tell the tale.

One final thing - midges. Take plenty of Skin So Soft, and a net for your head. And pray for a little breeze to keep the little b*****ds down.