I've been looking at demos and asked for opinions on the 1U reverb but it wasn't really what I needed. I would definitely recommend to make sure it suits your needs, I would personally not consider it as a sort of end of chain module. Again, that's just based on the small demo on Youtube and forum talk so to take with a grain of salt. I myself settled for a 2hp Verb for now, limited as well but at least it sounds decent and has that long tailed reverb I need. Now looking forward to real demos of the new FX modules by TipTop Audio. The ones I often see recommended are the Erbe-Verb by Make Noise (if only I had more cash and more rack space for it lol, demos sound incredible) and the Mutable Instruments Clouds (although a lot of people seem to use it as a reverb, it's wayyy more than that, again, wish I had the space for it).
For the sampling part, I haven't really reached a point where I'm ready to do that in my rack, I use an Octatrack in conjunction with the modular so I can't really comment further on that other than repeating that I would certainly try to decide exactly what needs to be achieved before looking at any module. There are a few options that are doing very different things so make sure you watch all the videos you can about those devices and also read their manuals before deciding.
For your pitch cv offset issue, I'm no expert so definitely check that out with someone else before making any purchase but I think a precision adder could solve your tracking issue. From what I understand, it is made to solve the problem you encountered and some modules have an offset built-in which could free up the Quadratt channel you are using now.
Discussing modular sequencers is worth its own thread (probably has several already tbh) but I'll just say that there are many many options, ranging from single modules to combinations of utilities, from immediate and/or random to pre-prepared sequences, some only cv, some only gate/triggers, some both. To illustrate, I was surprised to learn that you could have a lot of flexibility by having pitch and gate information being sequenced from 2 separate modules, or how it is possible to sequence a voice using a turing machine module in combination with a quantizer because those 2 aspects of sequencing are not really present in the "groovebox" world I was used to. Most options I know of in Eurorack take up a lot of rack space (because I need them to sequence more than 1 voice) so to sequence a single track, I can't really recommend any specific option.
All this being said, what are you using your O&C for ? From what I read in the manual (I don't own one yet, my 1U O&C is in the mail), the Quantermain app has a turing machine built-in so you could use that so sequence your other voice, and it has other options for pitch sequencing as well.
I hope this at least gave you more ideas and options to research :)
This thread has a link to my rack and a track I have on Youtube: https://www.modulargrid.net/e/forum/posts/index/8260