| A week has gone by with no replies, odd....
The string tension is going to be determined by the particular brand of strings you use. Since you have a fretless you may be using flats, which tend to have higher tension. TI makes flats with lower tension that many folks rave about. At any rate check around, getting the strings you like is step one.
From there you should follow setup guides. There are a few stickys at the top of the forum to get you started. Read them, find more info, ask questions if need be, but it's really not brain surgery.
What most of the sources don't mention are the particulars of setting up a fretless, and how it can differ from a fretted instrument. Assuming your fretboard is level (and a MIM should be decent enough), you can adjust your bass to your tastes. You said you prefer low action and low tension, which can be counter (keep in mind that lower tension strings will displace more than higher tension strings, meaning their 'vibrating arc' is greater). The lower the action the more tendency that the board will interact with the vibrating string. This can cause a rather pleasant "mwahhh" tone that many people go for, or if you go too far the strings will bottom out and it won't sound so pleasing. Your touch/playing style (i.e., whether you tend to pluck the stings parallel or perpendicular to the board, how heavy/light your touch is, ...) will have a lot to do with how low you can/should set up your bass.
But if you want really low action there's three things to consider. The nut is key, you can file your nut slots down nearly all the way to the fretboard if you so desire on a fretless. Second is the relief, and for fretless you can go all the way down to no relief (flat) if you so desire (although a bit of relief is more likely). And last is the saddle heights on the bridge. These are the proper order to perform the work, but you'll probably want to iterate on these (at least the last two) until you find what works best for you.
Note that changing your setup may alter the way you play - that is, in the same way that you can match a setup to your touch, you can adjust your touch through practice to match how your bass is set up. Again, an iterative process, but as you change setups you'll be a better player for your efforts.
Once again read the setup guides, find more info, search, ask questions along the way, and have fun with it! | 
