Your tank is now 3x bigger, so will take 3x as long to build up nitrate (you are looking at weeks ...) As long as you move your old filter (and ammonia & nitrites are zero), you won't have to worry about an uncycled tank. <Keep an eye on levels just in case, but I bet you will get at most a mini-cycle .... with only trace ammonia/nitrites.>
Also, you are feeding very sparingly (per your other thread), so the nitrates will come up even slower ....
pH of 7.4 vs 7.6 is within testing error, don't stress over it unless the pH continues to drop.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.