While I don't have the 50/1.4 lens myself, it's considered to be one of the best fast 50s around. Being a college student on a budget, this is a really good deal for what you get. See for yourself:
Pentax smc P-FA 50mm f/1.4 Lens Sample Photos and Specifications
Pbase.com is great for finding sample images taken with lenses you might be interested in getting.
The Pentax 18-55 kit lens is considered to be one of the best kit lenses among all mounts. Here's a review of it:
Pentax DA 18-55mm 1:3.5-5.6 AL Lens Review: 1. Introduction: Digital Photography Review
I've got one and even though I don't use it very often, I'm still very impressed with the images it puts out.
In the way of telephoto zooms, you've got a wide variety of inexpensive choices ($250 or less new) including the DA50-200, the Sigma 70-300/4-5.6 APO, and the Tamron 70-300/4-5.6. Personally, I have an older (vintage 80s) F70-210/4-5.6 which I really like as the images that come out of it are really sharp. Usually, you can find these used in the $150-200 range.
As for filters, I would recommend that you get a UV filter for each lens and keep it on the lens at all times to protect the front glass from accidental scratching. To answer your question, yes, you can use your 52mm filters with a 49mm filter diameter; you'll need to see about getting a 49-52mm step-up ring. If you're wanting to use filters like polarizers and neutral density filters, then sizing them to fit your largest filter diameter lens makes a lot of sense, money-wise, as step-up rings are a whole lot cheaper than getting more filters to fit every lens you have.
HTH,
Heather