It may not need any tweaking at all. What you want to do is to get a wideband reading at cold idle and while at WOT. As you'll be leaving the rest of the stock system in tack the ECU will be able to adjust for any other offset. The adjustments are just minor trims to the fueling. I don't think any one dial is capable of 10% (possibly not even that much). The high load trim is probably the only one which will need adjustment. Paying for a full tuning session would be a waste. If you know anyone at the shop all you really need is to do two or three WOT pulls on the dyno. After each one tweak the high load trim dial a little and you should have it spot on by/after the third run. If you're still uncomfortable then by all means pay a shop to do it... It shouldn't cost much given how little this needs to be adjusted and you'll already have it installed.
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