Let me go straight to your questions.
Indeed, RadMultiColumnComboBox does not have TextSearchMode property. However, you can set its AutoCompleteMode property to "Search". The Search mode filters and highlights the data. For a string property, the Contains operator will be applied, whereas for any other type the IsEqualTo will be used.
There is no out-of-the-box way of displaying the current item at startup. What you can do is to select the current item programmatically. Please check the Selection help article for a reference.
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