When do I need to follow up with fertilizing from this point forward. How many times per year and at what times?

I have some crab grass popping up on the side of the lawn that comes in contact with my neighbors lawn. What should I do to prevent this from taking over my whole lawn? I have done some spot treatments but dont want to kill my lawn at the same time.

Just want to mainly know what my next steps should be to help maintain my investment for years to come. Grass is a tall fescue.

The other crabgrass stopper is your irrigation. Crabgrass likes to be wet. If you are watering every day or even 3x per week, try to cut back to 2x or once per week. Allowing the surface of the soil to dry completely will stop crabgrass. Note that these approaches do not cost anything.

In general terms, grass needs fertilizer in the late spring and in the fall. 2/3 to 3/4 of the annual nitrogen should go down in the fall. For the late spring feeding I like to use Memorial Day as an easy day to remember.

Many (MANY) people fertilize in the early spring. This idea is reinforced by fertilizer company commercials reminding everyone to do Step 1 of their 4-step program. You don't need that. In the early spring the grass will come out of winter dormancy with a vengeance regardless of whether you fertilize or not. Grass farmers call this the 'spring flush' of new growth. In order to minimize the wear and tear on their mowers, they hold off on fertilizing until after the initial flush of growth subsides. Otherwise, if you fertilize early, you might be mowing 3x per week just to keep up with it.

If you want an easy to remember schedule, fertilize on Memorial Day, Labor Day, and Thanksgiving. If you want to try an organic approach, you may fertilize any day of the year without fear of harming the grass. Some people use organics every month to get top performance out of their lawns or to quickly improve their soil. Then in the fall they use a chemical fertilizer to "winterize" the grass. I don't think that is needed but hey, it's their hobby.

Keep an eye on your grass toward the end of summer. When the summer heat breaks is the time to add more seed if you need to 'densify' your fescue turf. This only applies to fescue and rye. Thin turf, even when mowed tall, will allow weeds in. Find out from your sod provider the EXACT seed used to grow your turf. Then find the best provider for that seed. Good, weed free, seed is more expensive than the seed you buy at the box stores or even nurseries. As you said, it is an investment. Don't invest in weeds.