1. In my experience, if you have to use it RAM Doubler is certainly a lot better than Apple Virtual Memory, but at the end of the day, there's no substitute for real RAM.
2. As far as the printer and modem ports go, there's really no difference between them as far as performance is concerned, they're both serial ports. As for the 7300 and PowerBook not playing nicely, you might want to consider trashing the File Sharing Prefs file or the AppleTalk Prefs file on both machines and having it generate a new one - one of them could be corrupted. Just be aware that doing this you'll lose all your AppleTalk network settings on that machine, such as what port you currently have LocalTalk set to use, computer name, owner name, password, etc.
3. You've got 8MB of RAM, personally I'd recommend System 7.1, its by far the most lightweight OS that will run on that machine, and if you do need a feature from System 7.5, most of the features from 7.5 can be retrofitted to 7.1 by installing the appropriate extensions or control panels. I have System 7.5.5 on my PB180c, which also has 8MB of RAM, and while it is very usable, it would probably be much faster under 7.1.
As for the previous owner installing 7.6 on it, it would've been via an external CD-ROM drive, or via a floppy disk install involving roughly 30 or 40 floppy disks from memory.
2. As far as the printer and modem ports go, there's really no difference between them as far as performance is concerned, they're both serial ports. As for the 7300 and PowerBook not playing nicely, you might want to consider trashing the File Sharing Prefs file or the AppleTalk Prefs file on both machines and having it generate a new one - one of them could be corrupted. Just be aware that doing this you'll lose all your AppleTalk network settings on that machine, such as what port you currently have LocalTalk set to use, computer name, owner name, password, etc.
3. You've got 8MB of RAM, personally I'd recommend System 7.1, its by far the most lightweight OS that will run on that machine, and if you do need a feature from System 7.5, most of the features from 7.5 can be retrofitted to 7.1 by installing the appropriate extensions or control panels. I have System 7.5.5 on my PB180c, which also has 8MB of RAM, and while it is very usable, it would probably be much faster under 7.1.
As for the previous owner installing 7.6 on it, it would've been via an external CD-ROM drive, or via a floppy disk install involving roughly 30 or 40 floppy disks from memory.