The LX200-16 OTA weighs 75 lbs and the upper fork assembly with OTA weighs 125 lbs. The entire scope with Meade's giant field tripod weighs 285 lbs. The RCX400-16 should be very close to that.
Getting 1 arcsecond RMS tracking from any Meade mount is very optimistic. Somewhere around 20-30 with PEC turned off would be typical. 5-10 with PEC turned on and everything carefully-optimized is more realistic. Under 5 would be incredible. This isn't an Astro-Physics mount, after all.
The CEM120 tripod and/or mount would not be capable of handling the RCX400-16. An Astro-Physics 1600GTO or 1100GTO or a used 1200GTO would be much more appropriate.
The 16" Meade LX/RCX scopes are way different internally than their smaller LX/RCX brethren. Be cautious with any advice/knowledge coming from the smaller models.
It is my understanding that Meade has abandoned the entire RCX product line. No repairs, no parts and very limited technical support.
The RCX400 electronics have always been problematic. There is a fellow that was selling an electronics repair package for the RCX scopes named Charlie Trump. I don't know if his kit is still available or if it will even work on the 16" model.
The biggest problem I have seen with the RCX models is the failure of the electronics controlling the three focus/collimation motors. I believe Charlie's kit was primarily to solve that problem.
Deforking a RCX is a bit of a big deal because of the collimation/focus motors in the OTA. Adding a motorized focuser to the RCX works. Collimation can be converted to a manual process where the shafts of the three collimation motors can be extended out the back of the scope, where they can be manually manipulated for collimation and focus preset. This is NOT a trivial project.
These scopes like to be balanced in both axes. When the clutches are released, the scope should stay put, wherever it is pointed. Or at least somewhat close to that.
A big problem with all of the Meade 16" scopes is the worm block assemblies. The mounting bolts become loose very easily. Loctite them in place. Use the non-permanent stuff. The worm block tension springs are too weak. Replace them. The worm block play limit set screws usually aren't set at all and allow the worm gear teeth to ride up and sometimes completely out of the worm wheel grooves. Set the limit screws so there is only a very tiny amount of play. Use non-permanent Loctite on the set screws so they don't drift.
Regreasing the worm drives while everything is apart is always a good idea. I use a two-part formula for worm drives A 3:1 blend of Lubriplate 105 and Nye Fluorocarbon Gel 868H. The 868H is rather expensive and hard to come by. I mix up batches of this worm grease for use in my day job and if you are interested in getting some, contact me off-list.
Do a careful PEC training run after the worm blocks have been dealt with and the balance has been improved on both axes.
You will want to use off-axis or on-axis guiding with this scope to get decent pics. Piggyback scopes for guiding will only lead to tears. A focal reducer will help significantly with getting good images. The really-long focal length of these big compound scopes makes everything more challenging.
I hope this helps.