I have no doubt about your ability to change the oil and filters, but one of the main reason we do PMs on forklifts is as much as is possible to see the future, is to have an expert look the truck over and catch potential failures before they happen.
as far as the intervals, grab the operators manual, and read it as if it was "gospel truth". it should tell you what to change, where the grease fittings are and what fluids to use.
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