As has been said, filler becomes a matter of preference or convenience, I use Humbrols which I find dries too quickly for my liking meaning I have to squeeze out very small quantities and work it very very quickly, however it's the one filler I can get locally so if I need some relatively quickly I know it's a short walk to the toy/hobby shop.
I've heard great things about the
Tamiya stuff and also mr surfacer 500 which appears to be more of a very thick primer, it's often used for zimmerit on tiger tanks etc.
As for cleaning, I keep the products simple, I use IPA (IsoPropylAlcohol), 90%, available from chemist/maplins/ebay for cleaning after acrylic, some acrylics get a flush through with a 6% ammonia and water solution first, (Fimo varnish and Citadel paints react with IPA and go 'claggy' (note technical term used there),
so flush with ammonia then clean with IPA
Enamels get cleaned with hardware shop white spirit or turps / turp substitute
Alclads/cellulose/lacquers get cleaned with Halfords cellulose paint thinner
I generally use cellulose to wipe the needle regardless as it will shift anything, this occurred after I wiped a 'clean' needle which was dragging a bit and the amount of unseen pigment on there was frightening.
This video is my procedure for a clean after a spraying session, (note, this is a session, it could be one use or several changes if it's a prolonged spraying day), I flush through inbetween paints with the appropriate thinner till it blows clear before using a different one but before the brush goes back in it's storage box it get a thorough clean like this, some people might consider it excessive but it's a hangover from my garage days when I used to have to strip and clean a spraygun someone else had 'blown through' with gun wash and considered clean, clean it before it goes away, it comes out ready to go and working flawlwessly.
Though it's a thorough clean, once used to the routine you can strip clean, reassemble and test your brush in 15 - 20 min easily.
Having ultrasonically cleaned my brushes in a Muc Off bath I can confirm barely anything came out so it clearly works.
The only difference now to the procedure below is that I clean the emulsion tube with an interdental brush, (0.6mm seems just right) and wipe the needle in cellulose thinner.
[video=youtube;k9YnScCetDo]