Vocals and guitars: yeah, fine, your only limitation is the sequencer. It handles longer recordings well, only limitation being flex space (around 5 minutes total if your recorders are dynamic, but once it’s recorded you can assign it to a static track so your buffers are completely free to record again.
Sequencer-wise: From small to big, you have 64 steps per pattern and 16 patterns per bank, 16 banks per project (to change project you need to stop the audio for a few seconds, meaning that most electronic music performers choose to have 1 song per bank. If you’re making pop/lofi stuff you can easily have 1 song per project therefore giving you tons of space and flexibility per track.
The other thing you can do to get around the 64 step limitation of the sequencer is to divide the clock speed of each track, down to 1/4 speed. So you sacrifice track resolution in exchange for longer patterns (effectively 256 steps per track at 1/4 speed).
Jam-friendly: very, especially once you get to grips with the crossfader. You can assign any number of parameters to each side, then morph between them freely. You can record in real time without stopping the sequencer, in a variety of ways (quantized, fixed length, etc). You can save 4 parts per bank, which remember the machine settings, allowing you to go crazy and change a ton of parameters in a frenzy of live editing, then reload and be back to where you were in a single button press.
Sample-based synths: it’s OK, kind of. You can load up single-cycle waveforms that loop, thus giving you some kind of pseudo-synth within an audio track. There’s even a project floating around called “monolith” which takes this idea to the max and turns the OT into some kind of 8-track modular synth. But I personally don’t find this very flexible or rewarding so I prefer to use external synths via the OT’s 8 midi tracks. This it does very well, because again, the sequencer is very powerful. It allows you to assign the knobs to control midi CCs of the receiving synths, so you can even plock parameters on your synth via the OT sequencer. Then you can record the synth back into the OT in real time into an audio track if you wish for more destruction. Very fun way of working!
Ableton and OT: not really. The OT’s main limitation in many peoples’ eyes is that it only has 4 outs, so it’s a bit of a hassle to get your audio out of the machine and into a DAW for further processing. Various workarounds exist, like doing two passes, it’s most tempting to do all of your mixing within the one machine. There are also sync issues, in that Ableton doesn’t really sync too well with external hardware. Easiest way is to just hit play in time on both machines and then record. I’ve made pop music with my OT but I like to overdub vocals and guitars in ableton after exporting the OT instrumental mix as a stereo track, because I like having more control over these sensitive parts of a mix and being liberated from the sequencer. OT makes it difficult to do little cuts and fades and comps that you’ll be used to doing on vocals if you usually work in a DAW.
LOFI: there’s an effect called lofi which offers sample rate reduction, bit rate reduction, distortion and an amplitude modulator with depth and speed controls which goes very fast for some ringmod-type sounds. It’s all a little digital sounding so if you’re looking for a lofi sound I’d do it outside of the box, with shitty mics, room noise, some cassette tape fuckery, etc. Do it on the way in and then sequence.
Arranger for pop music: do you mean the arranger in the OT or the sequencer? It has a feature called ‘arranger’ which lets you set up autoplaying sequences of patterns, BPM, etc. You can very easily rig this up to play a full pop song ABABCBA whatever automatically, without having to interact with the machine. Alternatively for live use you can use it as a simple backing track machine, loading up to 8 long stems (3min+ on average, but can be as long as you like until you run out of CF card space) and then just hitting play and letting it run through while you sing or play guitar or whatever. OT is supplying the backing tracks for my band this way and it’s working perfectly, although it’s slightly depressing to use such an expensive machine to play the role that an ipod could do just as easily 
Hope this was a bit enlightening for you. The OT is incredibly flexible and you can bend its will to almost any musical style you wish to make, once you learn a workflow and how to dodge its few limitations. As long as you’re up for working with samples and reading the manual several times, it seems like a good fit for you.
Question for you: how do you envision using the OT vs using a DAW? What are you hoping it will bring to your table that a computer is currently failing you at? What kind of music are you hoping it will allow you to create?
Happy to answer any more questions. Cheers 
