Maybe think about combining this idea, but get the Zoom B1-four instead of the B3n.
You can maybe go for a little cheaper cabinet, like if you are thinking $400 for a cabinet, maybe limit it to $325. Use the money saved to add the Zoom B1-four to the mix.
This way you get your Aux in, and you get the head you want, plus you get the multi fx to LEARN what you like. You can easily get $50-$60 for a used B1-Four, so you can just keep it as long as you are in the learning phase.
You will get to see if the Head works for you as a Pedalboard in every situation you need it for. If not, you have the Zoom Multi-FX processor to play with and see if, 1 - the Zoom and the MK500v2 are ENOUGH FX for you, or if you may decide to add a few modulation pedals and get rid of the Zoom when you do.
You will only need to bring the Head and Zoom to the rehearsal or gig, BUT when you go home, you will play thru the same set up (Bass to Zoom To MK500v2 To Cabinet) so it will stay consistent with what you do at gigs or rehearsal. Bass to Zoom to Head to Cab.
I realize the B3n is more of an investment, and in the end, may give you better performance if you really use alot of FX and Amp and Cab sims in the same chain you create. The Zoom B1-four and the pedal MS-60b I THINK have a little less processing power (maybe alot) then the B3n, but it doesn’t sound like you are going to max out the Multi FX with 5 pedals and an amp sim and cab sim in a single slot. FWIU, when you max everything out, you may experience problems with processing, and IDK how to say it in audio terms, but it would be like pixelation on a tv when the blu-ray or DVD can’t process all the stream correctly in the same time.
But again, I don’t think you will use the Multi FX like this. I think the Zoom B1-four will be plenty for you. Of course, I base this thought only from what I have read you write in this thread. If you do want to go crazy with pedals and totally changing your tone and sound altogether, with synthesizers and modulation, then yeah, I think you MAY need the B3n (but somebody else should verify this), but if you just want to add a little delay and reverb, maybe compression, you will be fine with the Zoom B1-four. I never had any issues when playing with it, and I loaded it up pretty heavy at times, but I was not using the Amp and Cab sims at the same time. I have heard those suck the most of the processing power.
Just a thought, but I think it gives you alot of the options you want, and it keeps you in a cabinet at home, which could help you to create your sound and more easily replicate it when you go play away from home.
If it ever comes down to it, taking a modern cabinet with you to a gig most likely will be easier to move around than a combo amp, as they are often lighter than combo amps. Plus this is not really the norm, it will only be if you go play a backyard party or something and there is no equipment and limited power and you have to take your cabinet. Otherwise, you will be set.