Hi Alan, You're gonna love you're new car, mine still puts a smile on my face every time I drive it, actually before that-even when I open the door and get a whiff of the trim!! I've just done the cambelt on my 99' Series 4 LS400, the interval according to Autodata is 63k miles or 7 years (whichevers the sooner), mine had one at 42k and has now done 103k, the belt I took off looked brand new still! I've had 2 Series 3's beforehand and did the cambelt on one of them too, the vvti (like mine and yours is a little easier than the earlier one-no distributor caps, leads etc), everyone makes a fuss about what a job they are, well Autodata give 2.8hrs, I guess if you did them regularly you could do it in that time, I'm an ex mechanic who's now disabled so I did it (and changed the plugs) over a day (with plenty of breaks!), any competent mechanic could do the belt no problem, they're a nice job actually, unless you drop something you can do it all from the top, just jack it up or use a ramp to save your backache!! Get the mechanic to follow the instructions from Autodata, you need to measure then compress and lock the tensioner for reassembly, but it's really straightforward, so much nicer than most front-wheel drive cars when the cambelt is all squished down against the inner wing! I've never removed the radiators, just drain the coolant (replace with genuine Toyota red coolant) otherwise you disturb the gearbox cooler pipes, japaneese radiators can get quite fragile over the years, check the condition of the water pump and idlers, a friend who's a technician at our local Lexus dealer guaranteed I wouldn't need to change any of them....he was right, they all felt absolutely perfect, there really would have been no point.
If I can give any more advice feel free to ask, I think the genuine belt which comes with reminder sticker and enough coolant (10 litres I think) came to around £50 trade, but it won't be much more retail I think they gave me about 8-9% off!