running schedule suggestions

I was just curious if anyone has any suggestions on my running schedule. I'm not training for a race or anything specific right now. Basically I've been trying to up what I can do for a long run with several other runs during the week.

Right now here it is: (right now I'm all on the 'mill, too, due to leaving the kids in the nursery)

Mon: 3 miles at 6.0-6.2 pace
Tues: 4 miles at 5.8-6.0 or faster sometimes, especially last mile or so
Wed: elliptical
Thurs: 3 miles at 6.0-6.2
Fri: 6 miles at 5.5-5.7 (I've been building up to 6 and have been doing 5 or 5.5 more consistently, got to 6 once so far but plan on it again this week)
Sat: elliptical (if I go to the gym, don't always on Saturdays)

So basically running 4 times a week, with the elliptical definitely one but maybe 2 days a week.

Right now it feels good, not having any problems. Does this seem like a good plan for general running and keeping at a good place for a long run?

Specific questions:

Should I up one of my 3 miles to 4 miles each week? Or both of them?

Shoould I keep trying to add on to my long run if I'm not specifically training for something? This seems like a dumb question, but do you know what I mean? I mean, what are pros and cons for continuing to add on and what would a general stopping point be??

I do want to do a half marathon in the "near" future. Maybe this fall, but I haven't found a close one yet. If I don't find one I'll definitely try to do one in March. But I wanted to really have a good strong base and wouldn't consider it until I could do 6 miles consistently, which I am close to.

Thanks for any input, thoughts, suggestions.