howdy darth ryl.
you ask an awesome question, which I hope means we'll be seeing you on the custom threads soon enough.
agis neugebauer and several others at lead-adventure.de and at cool-mini-or-not or boardgamegeek
have posted comparative images you might find useful.
these compare: ffg, WotC, West End Games, Knight Models, various gashapon: and a coin and a W40K guardsman for scale.
elsewhere, there are indexes of comparison photos by collectors of
"Star Wars gashapon correctibiru";
those host very accurate comparison images.
Most of those misc-disney figures from Star Tours or packs and so,
they're more comparable to the Epic Duels boardgame tokens,
or to the late-run WotC miniatures...
they are completely out of scale with FFG's Imperial Assault
though look alright next to WotC or next to Knight Models minis.
they tend to be on the smaller side.
Tangent: steer clear of Star Wars Command 'figures'
they're way too huge for use with anything!
they're closer to Armymen scale at ~1:33 ish
instead of 1:48ish/32mm.
The Tomy figures that other folks have shown here,
they're perfect scale! someone at Tomy was kind and was looking out for us!
I've already done what I can to efface Darth Kilogram and hack him up to make
other siths, it's a great outfit for customising.
BB8 is great for parts.
So, all you'd need to do for most of em,
is get some MDF round bases 33mm dia,
maybe the small base for BB8,
and paint the base, and glue your mini on to the base,
and you're good to go with an alright looking proxy
I hope this helps somewhat,
and happy StarWarsMiniatures-ing!