Just been reviewing this tutorial getting ready for this on a 04 Sienna, got the Gates kit from Rock Auto, and Timenkin and Felpro for the seals, had got the less expensive Ultra Power for the seals but after having to buy the FelPro the second time around on the the valve cover gasket that was undersized, I figured better be smarter the first time on the seals, thought the shipping cost determined using the different brands on my final choices. I am also buying the tools recommended that I don't have, along with the 20pcs seal puller kit off eBay, as I want to have all available options so as to get in too far over my abilities.
Sienna has 189k and I am not sure of the history, so I plan to start the job as if I where going to do it all with obviously taking the top cover off first and checking the condition of the belt and see if the seals are showing any signs of leaking, continue as necessary or in hopes of the previous owner having recently done the job, put it back together and drive another ~50k. I've been able to drive the van about 2 weeks and am starting to really like the 3.3, it does seem diy friendly though I find myself redoing things out of my own inexperience or frugal budgeting.