Why hello Deraj and welcome to my specialist subject area!
I play Skaven myself, also with a strong Clan skyre theme. There's a few tips and tricks that I can share with you in order to get the theme that you want but still not run the risk of having to convert every last damn model in your army. Are you sitting comfortably? Then lets begin! 1 - Height and depth.
Check out the pictures of skaven, Orks, Tyranids or even just regular hordes in the real world and what do you see that makes them different from the regular infantry? Height and depth. Think that a squad of clanrats is a little too uniform? I agree! Go ahead and grab a little bit of corkboard and stick some of them on that to provide a variance in the unit to make it feel more rag tag. Although another little trick that you can do is to stagger them in their movement tray. Depending on your local scene this may be seen as a no-no but in my group we measure from the edges of the movement trays, so that gives me the perfect opportunity to add even more chaos to otherwise roman legion-esque units. Get your movement tray and every other file stick a little bit of sprue there, just long enough to cover the 20mm length where the edge of the model should be. Make the end of the tray that little bit longer to accommodate this and all of a sudden you have a blob effect when the unit is ranked up with some slightly further back than the others. Add a bit of filler to the tray to cover the gaps and sand and paint as normal. 2 - Unit fillers are made of win!
Okay, so we don't want to have to convert the entire army to make sure that we either get a theme or an idea across to those that view the army, but we still want to get something going in terms of uniqueness. Unit fillers! Want that scurrying over idea to come across? Grab yourself a few 40mm bases and model a few scenes here and there, elevate them a little so that they are easier to be seen and viola! You have yourself a nice little eye catching min diorama to the unit. Create afew of them and it comes across the whole of the army at first glance and only really gets down to the nitty gritty when you look closer. Perfect for games where you and your opponent and 4 foot apart from each other. Whats more, here's where you can add a little clan skyre theme to the army. A giant cyborg Rat Ogre? Some diabolical dooms day weapon? Just let your imagination run riot!! 3 - Hey thats a nice front rank!
Yeah, this goes hand in hand with the good old fashioned method of painting the front rank to a high standard and just drybrushing everything else (pussies! Real skaven players wet blend everything!), but this time in the modelling side of the hobby. If you want to convert things, only do the first rank or so. Also borrows a little from the misdirection of the unit fillers option. Use some of the older warlock models as unit champions, give the occasional bionic eye or arm here and there, make the standard of the the unit some steam punk powered modern art monstrosity. Just a word of advice though: the Skaven don't see such advancements like, say, the imperium does. These are not bionic parts meant to replace lost limbs after combat. (for the most part anyways) Any skaven that is missing an eye or a limb is more than likely going to be eaten as the weaker member of the clan by some very hungry clanmates. They are seen as a means to improve themselves above what their bodies are currently capable of. However, it is worth mentioning a that a few crude replacements for the likes of unit champions could very well be in order, something quickly grafted on to not reveal any weakness to the his rivals. 4 - Go Nuts!
No, seriously, just go nuts. Grab yourself a jotter, keep it with you at all times and write down any silly old idea that comes to the front of your mind. Don't care what it is. Could be a warpstone powered lawn flamingo for all I care! Just. Write. It. Down. Then what you do is come back to that little scrap book when the idea well dries up. See what little treasures you have stored away that you might have forgotten. Hell, even add a few rough sketches to better visualise what you were thinking of at the time. I came up with my Warlords Warpstone powered, cog driven bonebreaker when I first saw the leaks of the Space Marine centurions, took the picture and scribbled all over it is MS paint. Randomly found it whilst cleaning out my hard drive a few months ago and it's now been made reality! If it wasn't for that then a good idea would have slipped through my fingers. 5 - Inspiration
. Thats all you need to get the ball rolling. Go and play a few games that have that clan skyre feeling to the environments. Bioshock, Dishonored, Guild wars, the Dwemer ruins in the elder scrolls. Not only can this serve as a leaping point for your own projects, but unlike a film you can get a full 360 degree view of the object rather than some passing footage. One good mention must go to Half Life 2, whilst the stuff in there isn't precisely what you would call a skavens heaven it does have some very succinct points in the developers commentary about how to keep something grounded in reality. Whilst we are dealing with a race of magic infused chaos ratmen in a totally different reality, we exist in this world and having things grounded in solid reasoning makes the conversions believable.6 - Contrast
. If you are wanting to make the army feel like a roiling horde of Skaven then make sure that you have contrast in your own army to make those horde units stand out more. Plus it helps them actually feel like the are meant to look that ragged!
Anything else that you need to know just ask. I think I might
have gone off on a tangent there....
Oh, and do yourself a favour - take your time and get the best job in that you possibly can. Sure drybrushing and dipping is easier, but no where near as rewarding as properly highlighting the models.