Sorry to hear the airbags are going. But easy fix to swap them out for coils. We designed the original bolt in coilover kit and I see your indicating getting that from us, thank you.
As for your specific questions, for the suspension kit you are describing the only key thing I would add at the time of install is replace the top strut hats or "strut bearings". The original rubber on them is usually tired and its worth the $50 for a set. You can get these off Amazon easley or your local NAPA. Since your getting new strut top hats, you can have a local shop assemble them for you, again some NAPAs offer this or just your local service shop that does struts. In our area its about $50 total to put a set together. This will make install easier for you as your truck is fully drivable up to install time.
Other Toyota part to get is a set of rear upper spring cones, you can get these from Toyota, a local wrecking yard (any 2003 + 4Runner, FJ Cruiser or GX460 base model will have them and its hard to hurt them in an accident outside of fire) Metal-tech 4x4 also has the custom made high performance polyurethane "Key Cones" developed by MT4x4 and Energy Suspension and made in the USA. The MT4x4 Key Cones come in all stage 2 conversion kits.
As for replacing rear links, adding adjustable panhard etc. My suggestion is to install the full suspension kit, then drive the truck. If you do the upgrades in steps you can track (feel) the changes in your truck. You can also troubleshoot issues faster if they are to come up post install. For example say you replace every bushing on your truck, do the suspension front and rear, all shocks and upgrad pan hard bar, but when your done you hear a clunk when you drive.... it is harder to figure out where that clunk is since you just had the whole truck torn down. Vrs. one system at a time, you know where the issue is as you just had it apart.
Now some parts like installing Upper Control Arms or UCA's is best done at the same time of the suspension install. This is due to #1 the UCA is very easy to get to when the front strut assembly is out and #2 you will have to pay for a 2nd alignment later if you do the UCAs separately. But lower links, panhard etc. all easy to add later as they are not going to effect doing them at the time of install or just doing them later. (at least it would not in our shop) Sway bar drops, again the trucks will work with the stock parts, you can decide as you go if you need to add extensions or drops. (I have not ran sway bar drops on my GX470 since 2015). I do agree with
@Rednexus on the tie rod ends. If your having a shop do the work, just have them check them to see if they need replacing. It will save your new tires. NOTE if you do, tell them you want your OLD ONES BACK! Yes you want them back as they are perfict trail spares! (its the inner tie rod you "might" need most likely.... guess how I know!) Tip of the day: Used take off mechanical parts are great low cost trail spares.
Dif drop kit: This is a personal preference for most. Me personally I just keep my CV boots healthy and dont over lift the front end. Fresh OEM Toyota boot kit for each side is a great way to go right from the dealer. ($65ish each depending on where your at) However the common diff drop kit like the Total Chaos 87200 kit does work and is not that costly at $38.48. But healthy boots and not over lifting the truck = no need for the drop kits. (Note: OEM boot kit to refresh your OEM CVs way better than discount auto store "reman" $75 made in China aftermarket CVs. Your stock Toyota CV/axles are way nicer! The cheep replacement CVs make a low cost trail spare)
If your looking for Old Man Emu suspension or OME actually in stock with a vendor, we have them! Also all ih8mud members get an extra 5% off with the code ih8mud.
We have in stock full OME kits with Med springs for your GX470. Also all full suspension kits purchased for a GX470 include a
free Metal-tech 4x4 stage 1 coilover conversion kit.
As of right now we have 16 of these full kits in stock.
Check out Metal Tech 4x4—your home for high end off road parts and accessories, specializing in Toyota. Browse our selection of off road products today.
www.metaltech4x4.com
As of right now we have 10 SPC UCA's in stock for your truck.
Gain an additional + or - 2° of camber and 0 to +4° caster change with the ICON Lexus GX460 & GX470 SPC upper control arms, available at Metal Tech 4x4.
www.metaltech4x4.com
We are also here to help with any questions drawing from our almost 22yrs of experience.