Savage 21 BL Conversion - From The Beginning...Advice Appreciated =)

Hi all, been a long time since a posted substantially in here! =)

After recently scoring a free savage 21 (from what i can tell?) I've made an order with mike for some parts to start on the conversion... I wanna build this to be a tough as nails, ballsy, bash capable machine =)

To make life simple (and not so harsh on my wallet at the same time!), i wanna run the same electrics i run in my LST...
Motor - Lehner 2230 11t
ESC - MGM-Compro 160-24 (i have an 80-18 car/boat, but fear it wouldn't be enough? - thoughts?)
Batts - 18x GP3700 packs (3x 6-cell packs in series)
I wanna keep the mech brakes, and utilise the reverse module too...

I'm in need of advice with regards to gearing and drivetrain parts, as this is gonna be my first savage! =) From what i can tell, there are many options to take, and most things i've read, people don't really say why they're doing what they do...

With the spider gears - you can have like, 4/6 and 8 gears right? what's the difference in strength between em all?

Also wondering about the 3-speed? Found one NIB and assembled for 80 bux on ebay... Does it require a whole new case, or is it still gonna be compatible with what i have?

Now... to the parts i have on the way...
From Mike...
*x1 FLM Tranny Forward Brushless Conversion
*x2 FLM Hybrid Bulkhead
*x2 FLM CNC Shock Towers
*x2 FLM LST Shock Conversion
*x1 FLM Steering Drag Link
*x1 MGM usbCom+

From elsewhere...
*x1 Integy MSR6 LST Silver Piggyback Shocks
*x1 RD Logics 23mm Hex Hub Extender w22mm Nut

I've ordered the "FLM Hybrid Bulkhead" but do you guys know if this part replaces the "FLM CNC Machined Savage Diff Cup"? I'm assuming so...

I was also looking at the FLM extended arm conversion, but wouldn't mind the uppers to be adjustable? Anyone know if the conversion includes adjustable uppers, or if it's possible to get them? I see the ones on rc-monster, but are they the same as stock, or are they extended?

Thanks for your help guys, i really need it... i'm not ashamed to admit it -lol- I tried on my own first and was just gonna post it up finished out of the blue, but figured i'd be best doing it once -lol-

Cheers =)

-daniel