Paulo, very well done, excellent work! I've always loved the Planet Suite and wore out my vinyl album listening to it endlessly as a young lad. You've captured Holst's pace and lightning-fast changes of ideas and feelings in Mercury.
I agree with William: I can imagine this eventually in VSL's music showcase. And I believe it may well happen once you're happy that you've ironed out the various midistration and mixing impedimenta - of which I feel there are still a few worth addressing. I'd suggest you take your time with it; I'm sure you already know that giving it a break while working on something else can sometimes work wonders when you get back to it with a refreshed perspective.
Up front for me in the few current impedimenta is spatialisation and reverb. The reverb you've added seems a little too cramped in size and width, which is emphasised at the wetness you've given it. I don't have MIR, so you describing what you've done with it probably wouldn't mean much to me.
I agree with you and think this piece can carry some big, wide, opulent reverb, such as in this fantastic real-life example I've linked below, performed by the UK NYO at the Royal Albert Hall in London. Holst worked within walking distance of the RAH and no doubt knew it very well. (No need to be daunted by the huge size of the NYO; I've attended a performance of the Planet Suite at the RAH given by a much smaller orchestra and it was truly superb. The Suite's orchestration is scalable).
The Albert Hall is different to most concert halls in that the stage is almost in-the-round, such that early acoustic reflections of the stage zone aren't so significant. Hence using Synchron Stage (or Teldex or any other scoring stage reverb) coupled together with a big hall reverb can't really emulate the RAH sound. Also the RAH's main auditorium acoustic reflections are somewhat unique in that they don't decay in the same way as in rectangular concert halls. If you fancy the RAH acoustics but don't have its Impulse Response file to plug into a convolution reverb, I can only suggest trial and error using the large-hall reverbs you have, making sure that Early Reflections aren't too prominent.
Your panning appears very good, but overall spatialisation might be enhanced if you use a few reverb plugins, all of the same space but each panned slightly differently, and send different instrument sections to each reverb, roughly matching up stage position with reverb plugin panning.
Also, I'm a bit worried about what seems to be a distracting degree of masking at various moments. But perhaps we can take that up a bit later when I've had time to listen closely and identify times at which it happens.