Is buying a used hybrid with 100k a reasonable idea?

You have to work within your budget. If that's what you can afford, then that's what you get.

In general, Lexus vehicles are known for their reliability, and a well maintained Lexus with 106k miles will probably still be very reliable if you continue to take care of it.

I would recommend doing research on that specific model - specifically the hybrid/battery systems to understand if there are any common issues you need to plan for. But even if you find a few common issues it doesn't mean I wouldn't buy the car - look at the cost of repairs and ask whether it would be cheaper to spend more money on a newer vehicle or just plan on paying some money to have those items repaired. In most cases its cheaper to just plan on having minor issues fixed than to spend thousands more for a newer vehicle.

If you want to save money or get a newer vehicle for the same price consider buying a Toyota instead. Toyota and Lexus share engineering so a Toyota Rav 4 hybrid is more or less the same vehicle from a mechanical perspective, it just doesn't have the luxury trim features you'll find inside the Lexus - which means you may find a newer one with lower miles at a comparable price.

You can get some great deals on 100k mile cars.  Lexus's are incredibly reliable, but you still have to know what you are getting yourself into.   On a 100k luxury car you have to expect $1k-$3k in average maintenance costs per year at a mechanic to keep the car in good shape.  This can still be significantly cheaper than spending the money on a newer Lexus, but if that doesn't sound affordable to you then you are indirectly buying more car than you can handle. On a 100k car you have to expect maintenance costs as almost a certainty, not just as bad luck. 

Not OK. It has high miles and an expensive battery pack.

No that is way to high for an electric car the batteries will need to be replaced soon 

Nope.               .