Buy moog end links when you need to replace. They're cheap and will last much longer than anything else.
The only thing about the focus is the difference between europe and NA foci. The focus the euros got are different, especially mk2.
I know some thing about focuses, but not a ton.
Basically:
MK1
Available in sedan (zx4), wagon, 2dr hatch (zx3), 4dr hatch (zx5)
2000-2004 2.0l vetec
2001 -2004 SVT Focus, 2.0L zetec tuned up by cosworth. 6 speed manual. Suspension upgrades, super nice exterior. Basically a totally different animal If you find one it good shape for a decent price, buy one. Don't mess with it if there are bad condition bumpers, highly desirable and very hard to find...
2004/2004 some focus had the 2.3 duratec. Same engine I had in the mazda.
2005-2007 ST - sedans, with some exterior styling, had the 2.3 duratec. If you can find one in good shape and for a good price, buy it. The prices of these have gone up from sharing the name of the new ST
2005-07 2.0 duratec. The engine I have in my current focus.
Basically the mk1 is really disorganized haha. I honestly don't think ford was expecting the focus to be successful here.
The first gen had a bunch of really weird special editions. Sony, street edition, kona, street appearance and more I couldn't tell you too much about these... I just know they're out there. Only a real enthusiast will actually be able to spot one typically. The standard owner typically don't even know what they own and won't advertise it...
Mk2
This is the focus I have. I have 09 coupe SE (with the SES bumper) with the black chrome headlights and taillights, IMO the most desirable mk2. I believe 09 is the only year that all coupes regardless of trim level had the nice bumper.
08-11. You can get them in either a sedan or coupe in a variety of trim levels. I don't think there were any special editions. Basically all the same car with the 2.0 duratec.
My biggest complaint with the mk2 is that it's really the bastard gen. The mk1 and mk2 are very similar mechanical wise, but everything else is kinda hard to source... especially since you need to distinguish parts for the euro mk2 which is completely different.
I think the mk2 looks better stock (with exception to the SVT) than the mk1. The mk2 interiors are much much nicer too.
The duratec is a pretty good engine, its used in a TON of vehicles worldwide.
Before the focus I had a mazda 3 that had the 2.3 and auto tranny. I strongly recommend MANUAL! The 2.0l in the focus may be smaller but its a million times better because of the manual transmission. Feels much more powerful and responsive.
The mk3 is 2012-present, probably out of your price range. These are tons better than the mk1 and mk2 though.
Not sure what else I could tell you, if you have any questions ask I guess. There is a good community for foci btw, focusfanatics and focaljet are good places.
I am looking to get out of the focus game though... and thats only because of fwd. I don't really like how it feels in deep snow...