I saw in your comment what you plan to do (and are doing now). That is a very reasonable course of action to get started with. Eventually, you will run into a problem with recovery. It's a fact of lifting for strength. I've recently had to make the transition from Starting Strength to an intermediate program which only provides gains once a week.
In addition to the Starting Strength, I do recommend you get the book "Practical Programming for Strength Training" by Mark Rippetoe and Dr. Kilgore. This will really help you make the appropriate decisions on how to tailor what you are doing to keep your linear gains working as long as possible.
Here's some general observations I've learned as I went down the same path:
- You can do the extra day of work for only so long. Eventually you will need that extra rest day. When that happens, you can stack the conditioning work after your lifting.
- Make your conditioning work with your lifting. High Intensity Interval Training (HIIT) is a good method to do that. You just want to keep your heart rate up within the Zone 4 range (anaerobic zone) to lower zone 5 (power performance) and take rest breaks as needed to reset to the bottom of zone 4. We're talking sprints, hill runs, sled drags, sledgehammer work, etc.
- Pay attention to the amount of sleep you get and the food you eat.
- As your squat gets close to the 300lb mark (I got as far as 310, others I know didn't break 300), you will have exhausted all you can do with Starting Strength.
There are other programs such as Madcow (intermediate-weekly gains, or advanced-monthly gains), and Wendler 5/3/1 (advanced monthly or 3 week gains). Wendler 5/3/1 has you lifting four days a week, and you'll be able to stay with that program (or variation of it) for a long time.
Just be smart and listen to what your body is telling you.