Transitioning to toddler bed

My oldest is almost 2.5. He’s still sleeping in his crib and sleeps all night. About 11-12 hours. But, I have an almost 3 month old that will need a crib soon and I’m hoping to use the same one my toddler is in. He is speech delayed but understands a lot.

Currently both beds are in his room. If I put him in the toddler bed, he’ll stay for maybe a few minutes before he’s running out of his room. His room is toddler proofed. So he can’t get into anything he shouldn’t be in (except maybe throwing his clothes around). He still takes a two hour nap also.

I’m hoping to get any kind of tips, tricks, or insight on transitioning him to his toddler bed. Do we start with bedtime? Naps? Take the crib down? I need all the advice.

TIA!