Hi - thinking of getting my 1st 'Reef' set up - initial thought was the 130d BUT fell in love with the 250 - would this be too much for my 1st go at the hobby ??
The 250 has a larger water volume and with marine systems you need to keep the parameters stable such as alkalinity etc., and the more volume of water the easier it is. With smaller volumes you can get quick changes which isn’t good.
My 1st tank was a RSM 130D, I started with it to see if I could have success... 34 gallon, then upgraded to the RSM 250 66 gallon, in hindsight I would have started with the RSM 250.
On live rock ... I went with around 66 pounds one pound per gallon, I like a more open look... (maybe 35 kg) or up to 50 kg - you can save some $$$ by going with s combo of dry rock & LR - I have done both & both work... my 130D all LR Tonga Branch $$$, my 250 20% LR and 80% dry rock
lots great soft coral choices (my favorites) ... zoas, torch, hammer, duncans, acans, so many...