To fit anything other than the stock speakers in the doors you will need adaptors, even for 6x9's. That being said, most 6x9's will be too deep unless you use an adaptor that spaces them out an inch and then you may need to space the window track back. My recommendation would be to go with 6.5's. The question then becomes whether to go with components or coaxials. Most components are going to be way underpowered running off the deck power. I have the 5500BHS and it is actually about 18 watts RMS. I know you're planning on adding an amp later on but I think you would be better off adding a 4 channel amp into your build now and power them right from the get go. I have an Alpine MRP-F450 laying around that I just took out of my truck when I put my Boston Accoustics GT4100. It runs 70 watts per channel RMS and even still has the box, manual, and endcaps (which are always missing). If you're interested in that, PM me and we can talk about it. The other choice is to go coaxials. Coaxials usually require less power and are easier to install because you don't have to find a place to mount tweeters and passive crossovers and run extra wiring to go from the crossovers to the mids and tweets. The down side is most coaxials don't have anywhere near the clarity and midbass response when properly powered like a set of components.
As for brands, it's up to you and your budget. The popular choices here for a less expensive build are the Polk Audio DB6501 components. These usually run in the $125-$180 range depending on where you buy them and the Infinity Reference 6030cs which run $120-$180 depending on where you buy them. The Hertz entry level components, DSK165, usually run around $199 and are very nice. A lot of people also like the JL Audio C2-650 components that are around $199. So, it's all up to you and I would recommend getting out to listen to some. If you are going to step up and buy some better components, you will definintely need an amp. I am personally running a set of Polk Audio MM465 Momo 6.5 components right now. They are the original Polk Momo components and are over 15 years old but still sound great. That being said, I am looking to upgrade to something like the Hertz High Energy components, CDT ES components, or maybe Rainbow or Hybrid Audio components. My only problem is that I don't have anyplace around to listen to the last two and don't want to buy something I haven't heard and don't want to buy something before I've heard the other two. All of those components will set you back over $400.
As for adaptors, you can get them from several different places and in several different flavors. I have TacoTunes adaptors that I took out of my Tacoma when I put the stock stuff back in and traded it in.
Use these products to install after market speakers into your Tundra. . I have the heavy duty plastic ones since they tend to repel water a little better than the MDF ones. There are also these:
Toyota Lexus 2002 Up Speaker Adapters Brackets Adapter Speaker Harness | eBay . They're not too bad, especially if you use some sound deadening and weather stripping to install them correctly. Of course you could always use the stock speaker as a template and make your own out of MDF.
