Sooo, I'm definitely NOT an "old hand", but as a "newbie" I tend to ask tons of questions... and asked a bunch of people at stores, fellow students & instructors a similiar question when I took a class I took a couple spring/summers ago & was building my rack. So here's my 2 cents.
One of the instructors told me that she & her husband had all kinds of stories of why they never climb without their .3 BD C4. I bought a .3 and .4 and was really glad I did.
Later wished I had something smaller for more shallow cracks but wanted to stick with flexible stems -- added a Metolius MasterCam yellow - love it!
If you decide to get more wire gate biners, BD Oz were highly recommended to me as lighter than Neutrinos & still insanely strong. I use them on all my trad draws & to rack my pieces. Seems like Neutrinos are the ones that can come color coded - I just added the color I wanted my Oz (ie if I wanted to easily see from the biner which cam was on it while it was on my rack) with a Trango rack tag. They come in a bunch of colors. Pretty sure I came ahead weight wise even with the weight of the extra rack tag & I like the feel of the Oz.
I also heard lots of good things about CAMP tricams & liked them when I experimented with ones that others had. Seems like people love them... or... really don't... so you may want to try out a buddy's. I got CAMP's 4 pack of pink, red, blue, brown & have used all of them. John Long & Bob Gaines (in Climbing Anchors 2nd Edition - great book if you don't already have it. Lots of great info on pros & cons of different gear, materials, great pictures on good & poor gear placements...as well as anchors) Anyway - they say these smallest 4 sizes are the most stable sizes when placed so I have stuck with just those. They are relatively cheap, small, light &, well, I think their action is super cool.
Last thing. I ended up doubling up on some cam sizes. I bought all my duplicate cams as BD C4 because I liked their features & acton & didn't want to have to debate which cam brand to save for further up the climb. However, C4's are quite a bit heavier than Metolius TCU's - & it added up that my rack is quite a bit heavier (& I think probably bulkier to cram into my pack) than my buddies' who stuck with Metolius. I think MasterCams were just coming out the summer after I'd already bought my duplicates, but if I were buying any duplicate cams now, I'd seriously look at MasterCams (flexible stems) or TCUs (non flexible stems) - for their lighter weight. I think I've heard Metolius cams tend to come with a smaller price tag than the C4's too.
Happy Climbing!