The build threads from both Homer and Red who pasted above are full of great info iirc, go to their profiles to find em, and you can see the progression in their builds and ideas from others. Great stuff and good info above from both of them. I love reading internet forums stuff and have been looking into all this for my '03 as well. None of the below is my knowledge - all thanks goes to the many posters and explainers from over the years.
The FAQ and link sections in this subforum and other similar ones are gold. Most of the paths you will want to explore have been pretty well documented. Hit
Lexus Owners - Lexus Drivers - https://drivers.lexus.com/lexusdrivers and enter your VIN and get a carfax if you haven't already to check service history.
Radio options to add bluetooth range from radio adaptors $30 to small wire harness devices $75-$200 to full NAV screen console replacements $500-$800. Radio and Nav can be tricky to replace with aftermarket due to system codependency of the climate controls.
The driveshaft lubing is 6 zerks total and you don't need two different greases, early manual had two different specs listed but later condensed down to one spec. Just use some form of NLGI #2 spec grease and you'll be good, moly or no-moly is your choice. Lube the spiders until they express (you will hear the crackle), opinions on the drive shaft lubing vary, most recommend either 1) lube until you barely see it extend, or 2) just add a few pumps of lube in. Excess lube packed inside the shaft can supposedly cause hydraulic-pressure that can cause damage.
Tons of threads on build options and tire sizes and suspension options here and at clublexus and lexusownersforum. General rule of thumb. lifts up to 2" don't require non OEM suspensions components, but above that you will need UCAs at a minimum and possibly more. 265/70 and 255/75 will fit in stock spare location, larger than that (<32") you may need to deflate and ratchet strap to fit or carry via some other method. Rear airbags can be directly replaced with Arnott or deleted and replaced with springs. OEM shock body replacements with on the fly electronic adjustable valving are $$$ so most people go with non-oem replacement if lifting or if shocks are worn out.
Later years with 91 octane recommendation also have secondary air pump (part of VVTI), '03 doesn't have that complication, no problems in the 15k miles I've put on my '03 running '87. They also have extra seals for camshaft when doing TB change that you may see in videos but doesn't apply to '03 even though they are all 2UZ-FE engines. If you're gonna do the TB, general recommendation is to do all the pulleys and tensioner and water pump with it.
Other common issues, gas cap o-ring develps leak with age and throws a code for evap system. Rad cap can be an issue with age. Like all aluminum/plastic combo radiators they develop leaks over time, so keep an eye out for slow leaks via reservoir levels, or pink cotton candy stains/buildup. Consider them to have about an 80k mile life. Get an ODBII bluetooth reader and app for use with it if you don't have one already.
Lots of fake parts on amazon and ebay unless buying from a known retailer. Don't be tempted by cheap lookalikes for mission critical parts. At the same time there is a ton of gx470/prado120 stuff on the chinese sites when it comes to plastic goods and switches that people have good luck with.
Brake booster pump is a less common but common enough issue you may see it. Refurbed brake booster pumps are available. Not many people talk about replacing the brake booster accumulator as well, but I think it may play a part with the booster pump burn out. The booster is the vibration you feel through the brake pedal. Health of the brake booster system is gauged by how frequently it runs, and for how long.
Alternator failure is common as well around the 150k mark, they just need new brushes mostly, so they can usually be serviced, but often people just throw in a new one. Some people upgrade to larger alternator depending on your electrical needs.
Dash cracks can be stopped if caught early by drilling or melting small holes at each end of the crack for stress relief, otherwise they will grow and spider.
Other common basic mods - rear diff breather extension, cargo platform/drawers, rear barn door fold down table, rear barn door strut, headlight polish or replacement, interior light & backing light LED replacement bulbs.
Bumper and wheel well mods can expose airbox to water resulting in hydrolocked engine. Water cross and mod those areas with care.
Seat repair - depends on a lot on your local shops capability, some people use leather off the third row, some buy leather aftermarket that needs to be installed by pro, some go wet okole or other neoprene cover. Using leather conditioner may extend the life.
Many 4th Gen T4R parts will fit, some will need modification.
