Suit jackets certainly can be worn with other things, but you're right, you do have to be careful. Can you let me know your husband's age and size? The last thing I want to do is recommend unsuitable attire!
Also, have you checked with a tailor that the pants cannot be altered? Most suit pants can be either let out or taken in by up to 1 3/4 inches if done properly, and of course the hems can be altered to suit length as well.
Ok, the dark blue subtle pinstripe, this is where the importance of your husband's age comes in! I would recommend using this for an informal/formal look and teaming it with a smart pair of jeans, and a formal work shirt.
Matching this jacket with a pair of formal pants will be nigh on impossible, but matching it with jeans and going for a casual yet still smart look is easily done. What you have to do is think about the accessories. As I said, a nice oxford shirt in either a pale blue or white, along with a pair of smart jeans and then a black belt and black shoes, either plain oxfords or perhaps a pair of suede loafers even.
For the glen plaid, this can be matched into something more formal and worn almost as you would a sports jacket. Pants will have to be dark, plain and pleated. I would recommend dark navy pants, and brown shoes and belt. In terms of shirt and tie, you can't go far wrong with a white shirt, and then a tie that brings out a bit of the color in the glen plaid, so a tie with a hint of red in would go nicely.
If you are looking for a more western interpretation, then you can find suits with a mandarin influence, or perhaps a Nehru style suit which fuses Indian themes within the suit style. I would avoid the white shirt/black tie routine, it'll either make you look like you're going to a funeral, or going to carry out a hit on someone!
What you need for interviews is something safe, but also nice and smart. You can't go too far wrong with a pastel blue (not a navy blue, more of a sky blue) cotton shirt with tie that has gold/yellow/blue in it. Alternatively a lilac shirt with a tie that has a combination of purple/blue in it works well.
A general rule of thumb that I advise is that the darker the shirt, the lighter the tie color to lift it. The opposite of that works too, i.e. if you're wearing a very light shirt, then a heavier colored tie is good.
I say go ahead and buy the suit. It sounds like a winner. There are always a lot of questions asking whether or not a double breasted suit is hip and I say it can be. It's a classic look that will never go out of style - although, sometimes the look is more "in fashion" than others. However, because this suit is a classic it tends to look better on men and not young men or teens.