Chadharrelson,
You can make this happen as the 5000 does not require the Mitel Border Gateway (MBG) to make this work; unlike the 3300.
Now, that being said there are some concerns as Chrismitel's answer suggested that there could be issues of Toll Fraud if it isn't implemented correctly and security isn't foremost in its design.
Your best bet is to open only the ports necessary for the 5000 to work with all of your remote applications and in the case of the SIP phone only allow specific MAC addresses to utilize those ports when going through you firewall. Also make sure that the password associated with your SIP phones are not the same as the extension and do not coincide with any numbers associated with the phone or the 5000 in general.
If you need to know specifics on the 5000 side after reading this then just post back.
Thanks,
TE