heres a basic shopping list of what you'll need , feel free to go and get prices for it all.
you can either buy a 2nd hand 4agze engine and use you 20v head and risk it or try and use some of your existing gear.
-your silvertop rods will be ok. they are the same as ae101 4agze.i use them and have no issues.
-8.9 CR 4agze pistons , id buy them new from toyota , go and price them
- trd headgasket might come in handy for reliability sake. i use 0.8mm 3layer steel.
- for power up to ~145kw use tdo4, t3, t25 turbo , for higher power use tdo5 , t3t/4, t28, vf24, ht18. i wouldnt bother with an external wastegate unless you were considering running over 17psi on any of the larger turbos.
how much power you want? if over 150kw atw then you'll need larger injectors ~($200-300) and probly a larger fuel pump (~$270)
go for a decent i/c with not too large a core size , around evo size is good but dont rely on old 2nd hand ones to be efficient. (~$250 off trademe)
dont cheap on joiners , 300ish worth of samco joiners to plumb in a typical front mount setups worth of stuff.
you will need an aftermarket ecu , to run vvt and be able to tune for boost etc. allow probly 1500 for an ecu and wiring on top of that. id allow (~600ish) for tuning too.
fabrication- can you weld effectively? you need to allow for the fabrication of i/c piping, exhaust manifold,inlet collector, piping for air intake, oil drain to sump etc what you spends depend on what you can do yourself.
id also leave myself up to 1k for random shit that you never thought about at the start,

because something always goes wrong. ive probly missed loads too , thats all i get off the top of my head.
it helps if you ask specific questions too , not just , what do i need to turbocharge my silvertop?