I love the sound of blackface Fenders with reverb, but after getting the Malekko Spring Chicken I don't feel like I need real spring reverb and all the associated complexity and increased delicacy (I've had trouble with reverb pans.)
There are also an abundance of great tremolo pedals. I love tubes, but the less tubes you can use and get away with the better in my opinion.
I think a well designed effects loop that you can switch in and out of the circuit would be the best idea, if it makes sense in your new amp.
generally find the on board tremolos not to be usable in playing, to much, to little, never could get it right, had a custom Vibralux, and pro reverb, the on board tremolos were useless.
As far as reverbs, the spring reverbs really not that great with the boing and twang, they can be tuned to elimate that, Jim Price does that as part of the omega mod, but getting a reverb pedal like the holy grail probably a better option, unless you like the boing and twang of the spring reverbs.
What I like to see added on Tweed amps is a line out or slave out(with pot) so that effects can be added further in the mix to add more versatility thereby using the amp as a building block for tone.
No tremolo, since it's an effect that is used sparingly, if at all. There's plenty of tremolo pedals (both tube and SS) to choose from, if it's needed.
As far as reverb, a nice, resonant pine cabinet will give a quasi reverb-like tone, so no need for on-board reverb either.