For a busy time, I would do the 5 day hopper. We were long time WDW people that typically stayed 8 nights. For DLR, in the summer we typically come in on a Saturday and are in the parks by 2:00 p.m. We spend 3 full days in the parks and then on Wednesday, we usually spend half a day in the parks and then drive to the San Diego (or LA) area and spend the next 3 full days there. We were just at DLR last weekend-- we had to come to CA for something else so Disney was a bonus and we spent from about 1:00 to midnight on Saturday and then all day Sunday and Monday. We felt like we needed one more day--- we had to remind ourselves this was a Disney bonus, not a Disney trip!
Definitely get the hoppers--- hopping now starts at 11:00 a.m. To a WDW person, DL/CA feels like one park. The walk between parks is shorter than most walks from the bus stop to the gate at WDW. It is just a plaza between parks. You can literally be out of one park and into the other in less than 5 minutes. We have travelled from the back of DL (Small World) to the back of CA (Pixar Pier) in less than 10 minutes. Also for Spring Break, you definitely want Genie +. Once you have scanned into a park, you can book a lightening lane in either park. Also, at DLR Genie + includes all your photopass pictures, so you can make it worth your while by taking a ton of photos, even if you don't wind up using that many lightening lanes.
If you are wanting to go to a bunch of things in the LA area, you might want to consider staying close to DLR for the Disney portion of your trip, but having a hotel near the LA area for the other part of your trip. The drive between Disney and the Universal Area (which is close to Hollywood, Warner Brother Studios, Griffith Observatory, etc) took us 1 1/2 hours to get there at a non rush hour time, and on a different day it took us 2 hours to get back on a non rush hour time. The traffic can be a nightmare.
What all do you want to do in the LA area? We had no problem doing both the Warner Brothers Studio Tour and Hollywood in one day, and I think we might have been able to fit something else in that day too. We spent a lot of time at WB (probably longer in the wander yourself area than most people) and we did Madame Tussards in Hollywood, in addition to spending a lot of time walking around the Hollywood area.