Before moving to advanced services feature set from base, I believe you need a feature license for it.
Personally, to save on licensing and maintenace costs, I use whatever feature set provides the features I actually require. So, if base is all you need, no real advantage using a higher feature set. (More advanced feature sets also often require more flash and/or RAM.)
As to the best was to upgrade, generally across an Ethernet port using TFTP or FTP works well. With the later ISRs, like the 3845, I believe you can also copy IOS to a USB stick. With a current ROM image, you might even be able to boot from it too.
PS:
"Also, Do I WANT to over write the IPBASE, if I don't I don't have enough room."
It's often nice to have a backup image, but assuming everything "takes" with the copy, shouldn't be an issue.
"So If I do a "copy tftp: flash: and replace my base software with the advipservices software, and reboot, will i expect it to boot up in the new IOS?"
Usually, but if the former IOS is still present, router will boot into the first valid IOS image it sees unless overridden with bootvar. If bootvar is used, you can (still?) have a problem if specified boot image isn't found and another valid IOS image isn't found on default boot device.
PPS:
BTW: Don't erase the newer flashes. If they are "formatted", you can delete individual files. To totally clear flash, format it. (Believe format command uses newer flash file structure [DOS like] vs. older erase command.)
