Sure, but you have ~ 1000 albums. Many were purchased new and you looked after them. Would used record store purchases, generally speaking, require some attention? I wouldn't know.
Might be stating the obvious, but in general 2nd hand record shops, i.e. places that exclusively deal with music, are probably a more reliable source of good quality used LPs as that's their bread & butter. Whereas charity shops and any place where used music is just a part of what they sell won't be taking the same care with the quality of their stock. When I go to San Francisco I always like to plan a day in Amoeba Records, and all the second hand records I've bought from there I find to be in VG+ to mint condition, presumably because they examine and grade what they buy in. Can't imagine the British Heart Foundation doing the same thing (no offence them as a charity BTW). Oxfam is an exception as they do have dedicated music shops (we have one here in Southampton). Not sure what the situation would be with you over in Belgium but I would expect similar.
Most second hand shops usually display their grading on a label somewhere on an outer sleeve. Of course every place will have their own interpretation of what is "VG+", "EX-" etc but it's a guide, and I suppose you'd get used to a particular shop and how they grade over time. Do you get any record fairs in Belgium? That's another good source of LPs if so, and the same grading system applies here too. Online auction sites can vary, there's some serious sellers who also adhere to the same principles, whereas individuals and smaller sellers probably don't.
And FWIW my observations on your points would be:
1. MC in general is superior in sound to MM, but not always. MM has the benefit of replaceable stylus.
Already given viewpoint on that one
2. Suspended TT are possibly better than Non, but increase the amount of finagling required.
Not always. A non-suspended deck on a clever isolation platform or heavy shelf (or wall shelf) could perform as well as a suspended design in terms of isolation. Suspended decks do, however involve a degree of "faff" that you don't get from a non-suspended design
3. Belt drives can be finicky.
Yes and no. Rabs' Well Tempered and my Voyd are perhaps examples of "proper faffing required" (although once set up, probably don't cause any issues). Any deck where the motor-to-platter distance is fixed and the belt goes round the edge of the platter is the other end of the scale, fit, forget, simples
4. Project does not get much love from "serious'' TT people.
ProJect is a brand, much like Q Acoustics, that many (not all) get a bit sniffy about, as though they "only do cheap" and don't count as serious hi-fi, even at the top of their range. It's probably an image thing as much as anything, if it's sold in Richer Sounds it can't be serious hi-fi. I'd say that they are as serious as any other manufacturer. Of course whether or not you like their sound is a different matter, and I certainly wouldn't dare to infer that anyone is wrong for finding their sound bland or anything else, but keep an open mind. The Signature 10 and 12 are hardly bargain-bucket territory (£4250 and £8000 according the Henley's pricing) and although I've never had the chance to listen, I can't imagine they would disappoint
5. Album quality whether, new or old varies wildly across the range. Best bets tend to be older pressings form analog tape, but again not always.
Yes, there are some sensational recordings / pressings from the 50's and 60's, certain labels have a reputation for quality (Tamla Motown, Decca) but again, all that glitters is not gold. Similarly, Mobile Fidelity and the Abbey Road half-speed masters range should be excellent modern pressings, but not 100% guaranteed. It really can be a bit of a lottery (and an expensive one if dealing with new)
6. Chances of hearing an enhanced emotional connection with Vinyl over digital, on par with changing from solid state to full tubes, is possible but will require A LOT of effort.
Some of the best music (note: music, not sound) I've heard at shows has come from the simplest systems, with low price tags and relatively unsophisticated equipment. Not the most accurate or revealing, but the most enjoyable from an "Am I loving the music? Yes I am!" perspective. A well-chosen entry level turntable with a decent cartridge + modest amp + modest speakers = fun and pleasure. Unpretentious, is probably the way I'd describe it. Honest and rewarding, like comparing a '67 Shelby Mustang with a 2020 Ferrari Portofino. The prancing horse is measurably faster, more accurate, more capable, more exotic and has huge kerbside appeal. But does it stir the soul in quite the same way? Of course a budget turntable is going to be shown up for its limitations if paired with esoteric kit further down the chain but you get my meaning I hope
7. Hunting for nice records has many limiting factors (mastering, quality, where pressed, etc.) but is FUN. (it would be for me)
Absolutely yes! Be prepared for some disappointments along the way, but finding something rare and in good nick is a pleasure you can't really measure
8. For those who scoff at synergy of a full system, synergy between the four main parts of a TT set up is important. TT, phono stage, tone arm and cart require careful matching and can be changed to create different overall presentations of the music.
Different ethos(es) abound as to what is the most important part of that chain, but getting a physical match between arm and cartridge, and getting the alignment correct, is probably the most important bit to get right. Followed by getting the electrical match between cartridge and phono stage / SUT. And yes, it CAN be a pain in the derrière
9. Record cleaning machine is pretty much mandatory for someone who has to start buying second hand vinyl.
Depends how much you like clicks and pops! I'd say a big yes, a lot of 50p charity shop finds have been salvaged by my VPI.
