NP!
Ok so Stellar Labs helped me with the Pressure gauge. He let me know which hose to cut and what to insert in between. Here is a small album of pictures of the insides of my Gaggia.
It shows what hose I cut and what I attached in between. In short, I used this 3/16 barb to 1/4 NPT and attached it to the pressure gauge. And this 3/16 Tee Barb to split the hose to the pressure gauge! And just routed the gauge to the enclosure.
Dimmer was easy too! I followed this guide by /u/jasparaguscook! It's super easy and easily reversible. The dimmer has 2 cables. After opening up the machine, you disconnect a cable attached to the pump in the back of your machine and attach one dimmer cable in its place. The other dimmer cable connects to the original pump cable. So you're attaching the dimmer in between the pump and the original cable. here's an update to Jasparagus's guide with some nice pictures! The difficult part in this one is disconnecting the cable from the pump (tight spot!) I had to unscrew the 2 screws holding the pump and lift it up slightly at an angle to take it out. Jasp was able to take it out with some tweezers if I recall, lol. And also priming and attaching the spade connectors was completely new to me, but only took a few minutes to understand.