@Jamie,
If you have Premiere Pro and AE installed as part of the Creative Suite then the memory allocation setting in Preferences are set for the entire suite and not only for PP.
@BJBB,
1: When you right-click on a clip on your timeline in Premiere Pro and select "Replace with After Effects Composition" it immediately allows you to save the new Project it is creating. It then imports the clip or clips you had selected in PP, creates a new AE comp in the project you just had to save, and adds the clip or clips to this comp. The comp will match the settings of the PP sequence the footage was in when you initiated the replace command.
2: Once you make your adjustments in AE and save the project, those changes should be visible when you return to PP. Keep in mind this operation is not affecting the original clip in your Project panel, only the one or ones that were on the timeline.
You should also notice that there is a new AE comp icon in the PP Project panel. It will be named after the Premiere Pro project name and have the phrase "linked comp" at the end, for ex. "project01 Linked Comp". If you have closed the After Effects project you can also right click on the linked comp in PP and choose Edit Original from the menu that appears. This will reopen the AE project and allow you to make most adjustments.
**On a side note, sometimes I have noticed I have to scrub the playhead in PP to make the Program monitor refresh to see the changed I have made in AE.