I received your (the OP's) email about this last week, but was away cycling in Mallorca until yesterday (as I mentioned in this thread), so couldn't respond until now.

I know most of the roads you're talking about between Chateaux d'Oex and Luzern, and have a few comments.

If you're using a road bike then, as others have mentioned, don't follow the national cycling routes, but merely use them as a guide/suggestion. They often take you to roads that I don't consider to be the best option for riding on (which could be for any or all of the following reasons: too undulating, too indirect, too steep / inconsistent gradient, not surfaced). The section around Lake Brienz is particularly problematic - the route takes you along the south shore of the lake along a very steep and unsurfaced track. I've not done it myself, but I didn't like the look of it on the map, and then someone told me what a nightmare it had been for them. I've always gone along the north shore of Lake Brienz, which is a great ride, traffic is not too heavy because a lot of people use the motorway instead.

Coming from the north, the Brunig pass shouldn't be too hard of a climb. Again, there is a motorway to take a lot of the traffic, so you can happily use the other major roads. Towards the top, the motorway traffic will merge with you, making that section not so much fun, but you just have to get it over with.

From Interlaken to Chateau d'Oex will not be very difficult in terms of climbing. After Spiez the road slowly climbs up the valley until it reaches a height of about 1200m between Zweisimmen and Gstaad, a pass called Saanenmoeser (but sometimes it's not even listed as a pass because the approach from both sides is not very significant). I believe the national cycling route takes you along some back roads for most of this route. However, it looks complicated and much slower than the main road, so I've only ever used the main road. There's a reasonable amount of traffic, so I don't take it for fun, just to get to and from nicer riding areas. Plus, if you're riding up from Spiez you'll be on the road for much longer - I would plan my route to make sure that I was riding down that road instead of up, making the speed difference between me and the passing cars much smaller, and the time spent on the road much shorter.

On the last day, leaving from Interlaken, as suggested above, following Thunersee would be nice, then if you want to do some climbing there are some low passes (about 1000m altitude at the top) into the Emmental region, or you could just follow the Aare river to Bern and beyond, and take the train home whenever you've had enough. If you follow it to Biel or Solothurn then note that the trains from those towns back to Zurich are ICN tilting trains, and at this time of year you now need a special bike reservation to take a bike on those. It costs 5 CHF on top of the normal bike ticket, and has to be made 30 minutes before the train leaves; yes, I agree, it's very annoying, but fortunately the ICN's are the only Swiss trains that this applies to.

You asked about altitude profiles. As dakman mentioned, CyclingCols is useful for this, and also try ClimbByBike - just search for the name of the pass and you should be able to get the profile of the major roads going up to it. All the roads that you've mentioned will be open, but if you ever want to find this out for other major passes in Switzerland, then check this website.