Transitioning from Lost Mine of Phandelver to Out of the Abyss with level 5 characters

My party of 5 just finished LMoP and we’ve bought OotA.

The beginning of the book is important to the whole story, as is the feeling of desperation as they run low on resources, chased by a powerful enemy they can’t hope to match at this stage.

I’ve spoken to the players, and they’d like to continue playing their characters they’ve grown attached to, so I’ve told them I’ll need to temporarily depower them, if they want to get the most out of the book. This’ll mean taking some of the magic items they have (they found most of the stuff from LMoP, plus a few extras I threw in) and restricting access to spells/extra attacks.

I’m going to have them jumped by the drow in the middle of the night in a very one sided ambush, just to really push home the threat of the drow, but make it clear they’re trying to capture, so no one gets killed.

My question is, how much should I take off the players, and how should I do it?