Kellie,
I did a rigorous testing, your server is absolutely fine, the Joomla installation over which you were trying to install sellacious has issues.
1) it is not fresh joomla
2) it seems it is installed by using Fantastico software, it modifies joomla a bit and few big extensions like sellacious may find trouble on fantastico installed Joomla
I just freshly installed Joomla on your server here:
https://unusualstuff.com.au/j348/
where both joomla and sellacious working fine.
Sellacious Backoffice:
https://unusualstuff.com.au/j348/sellacious/
Access will be messaged you
I installed Helix3 template for bit broader look.
Sellacious Frontend:
https://unusualstuff.com.au/j348/index.php/myshop
Let me know if you need any further assistance.
Thanks & Regards
Abhishek