Some random thoughts:
When attaching a content database to Sharepoint the SQL Log file can be the same to twice the size of the current data size. the reason for this is that sharepoint takes an internal backup of the data verifies it (as well as some other magic) then attaches it to sharepoint, once attached the backup is removed (you may need to shrink the log)
Suggest using command prompt to attach rather than UI. run “stsadm.exe -o addcontentdb -url http://yourwebapp -databasename WSS_Content_yourwebapp
To attach a content DB of 100GB can take between 30 – 1h 30m depending on the hardware (for a resent attach I performed it took 1h 30min) and can consume between 60G – 200Gb worth of Tlog (for a resent attach I performed it consumed 79GB)
Note: Tlog will still grow in simple mode
Suggest keeping content databases to 50Gb (100Mb being the Microsoft maximun recommendation)