To be fair, 40 bottles in the cellar is already decent depth.
Rather than adding what some strangers on the internet think, I’d suggest letting your palate drive the direction, and where we may be of more help is where you say e.g. I didn’t much care for that because of…, but I loved the … in that wine.
Of those you have, I definitely wouldn’t wait any longer on the 1997 colonello. Indeed I’d be very intrigued how you find it, as I had very poor experiences with the 1997 cicala from the same producer (and only slightly better with their 1998 Bussia Soprana). It was very much when they were experimenting with modernist techniques. A shame, as I’d previously loved their wines.
Marchesi di Barolo 2000 Cannubi probably next to dive into, as although it’s a prestigious vineyard, 2000 is a warmer vintage and not one I’d be banking on long term ageing, plus I’ve found their recent style to be rather open. Oddly another where I still have fond memories (my partner’s first Barolo was one of theirs, and we’ve also had some good very old bottles), but I’m not excited by what I’ve tasted from recent releases (past decade or two).
Fontanafredda probably next one after that, as although 2006 quite a structured vintage, if this is the bottling I’m thinking of, it itself won’t be firmly structured.
I think these three might be useful in informing you how you feel about age in nebbiolo, and also more modernist in Aldo Conterno, vs. more traditional (but open) Fontanafredda and Marchesi di Barolo. The more older examples you can find, the better it will inform your buying, and there are specialist shops and/or auctions that can get access to them.
Cucco also of interest, as whilst we were disappointed when we visited in 2012, the company changed hands maybe a year afterwards, hence my interest in whether the new owners have re-invigorated the estate. 2016 ought to be way too young to drink though.
As for good/bad, despite having my opinions above, I’m very much a believer in good/bad for us as individuals, rather than some general ranking system. I know my tastes lean towards firm structure (but I love some florals as well), so some I like e.g. Marcarini, old Borgogno, La Ca’Nova may not be appreciated by others.
I do very much hope you enjoy exploring nebbiolo, be it Barolo, Barbaresco, Roero, Valtellina & Gattinara and others from the north, or indeed from elsewhere. In that journey, I’d also recommend finding 2-3 langhe nebbiolo wines you like, as there are some lovely ones around, that will be approachable earlier, but very much give a strong hint at what you expect in Barolo & Barbaresco… and a lot cheaper!
If you can ever find a way to visit the langhe (barolo villages, barbaresco villages, and much more) I’d strongly recommend it. It allows for more focused tasting across communes, vineyards, producers and 2-3 vintages. On top of that the food is some of the best in Italy, plus shared ownership of vineyards requires open access… thus its criss-cross of paths through these famous vineyards provides a wonderful resource for tourists who love walking through them (plus a few woods etc.). The villages are generally compact and subtly different, and it’s also easy to drive in (but the public transport is virtually non-existent). Langhe, roero & Monferrato tourist board is exceptionally good / professional.
Oh and welcome! You’ll find lots of fellow nebbiolo fans here.