LDF files vs. TRN files vs. Tempdb.MDF+LDF files.:
A few notes here:


You definetely have to separate the files logically using different partitions (I recommend separate partitions for: system, data files (mdf/ndf), transaction log files (ldf) and tempdb files (mdf/ndf). Where you put the tempdb transaction log file is up to you (tempdb drive or log drive), I'd go with log drive.
Backup files should not be on the located same device and especially the same VM (I recommend a different SAN/NAS).
Placing your data, log and tempdb files on different drives is mostly a way of improving performance. Transaction log is heavily written and is probably the slowest component of SQL Server. The second bottleneck is by design the tempdb database. If these 2 components are placed on different drives (especially if they reside on SSD/RAID10 disks), the performance will be definitely better.
You can keep the transaction log and tempdb on the same array as the user database files if you aren’t experiencing performance problems (at least not yet). I would look at the sys.dm_io_virtual_file_stats DMV to verify if there really is a problem with IO performance.
If you want to move these files to a different disk in a virtual environment you can create a separate virtual disk for every partition you want to move and assign these disks to different LUNs in the array.