Congrats! I purchased a 2004 Islander last year as well. I have changed over and added some items too. As far as the electronics go, I wish GW had a better setup for a dashboard style for flush mounting; but back then most of these electronics didn't exist. I'm in the process of using the "cubby hole" to flush mount my GPS/Fishfinder. I tried last season with it inside, which is nice and out of the way, but not very convenient while underway. I have removed the top and bottom covers and plan to use that as a template and simply flush mount to a piece of Starboard or similar material. I have the VHF in the overhead box on the port side and a large screened chartplotter that came with the boat on the starboard overhead. I added a solar panel on top of the roof, which helps out if I'm at a mooring or just want some extra electrical insurance. I also mounted a new radar dome that can be seen on my Garmin screen in the cockpit dashboard area where the cubby hole is getting flush mounted.
I'm not sure what pump you mean, but I also removed the hydraulic trim tab pump and switched over to electric trim tabs, much more responsive and no maintenance. The new found space (under the starboard berth) was quickly consumed with an inverter so as to run microwave, and other features whilst underway. Good luck, I wish I had some pics.