Changing the OIL is FUN and EASY... well its easy... i dunno about fun...
you'll need 6qts of 5w-30
I used synthetic oil... what brand you use is all up to you. (amsoil, mobil one, castrol ect...
The filter type if you're not using an OEM filter is 3614 (Fram) I believe...
You don't need to change the drain plug gasket after every change... its just just a washer...
There are plenty of DIY post around here or on the other lexus forums but I'll just give you a quick run through...
secure the car on jack stands or ramps... make sure your parking brake is engaged firmly if you're gonna use a ramp...
open up the filler cap, slide under the car, remove the drain plug, i think its a 14mm socket, I don't remember, its probably smaller if anything...
let it drain for a few minutes....
unscrew the old filter (counter clockwise) be prepared to see some oil spilling...
dip your finger in some new oil and lube the gasket on the new filter, put the new filter on, tightly, but not too tightly...
clean the drain plug and the area around the drain plug and put the plug back on.. once again tightly, but not too tightly, you really don't want to strip anything.
grab a funnel add 6 quarts assuming you let all the old oil drain out... you can go 5.5 then check the dipstick and add more slowly to suite...
start the car... let it run...
check for leaks...
no leaks... great...
you're good to go.
I could go into more detail and suggest you wait a few minutes so you don't burn yourself on a hot engine... but you should know that...