I had an IS250 SE-L Auto for 8 years and it was a brilliant car and completely reliable
As mentioned above, I would avoid the manual. It wasn’t very good and comes with road tax implications. If a manual is a must then I would look for another car.
I have a young family and the IS just wasn’t big enough. Luckily we also have an RX450h so that was used most of the time with the kids. The times that we used the IS as a family car, it was a very cramped experience and I’m only 5ft6. We replaced the IS with a GS last year and find that it has plenty of room for the family.
The Multimedia Package ( as it was named on the early models you are looking at) was available as an option on all grades IIRC, and came standard on none. It included Sat. Nav, the Mark Levinson Audio and reversing Camera.
The Suede seats were only available on the Sport trim. I would go with the leather. Ours had done 110k miles and the leather still looked good with very little wear even on the drivers bolsters. The Suede seats were only heated.