Light kitchen remodel without a contractor?

You are right that working as the general contractor yourself will save you money. Although you said it's not a full remodel, knocking down a wall and building an island involves moving around structure of the house, so you'll need to get permits and manage different trades people. It is a full time job trying to schedule and manage all the trades, permits, inspections, and a million other designs related decisions, etc...If you have never done a remodel before and your budget allows it, it's better to hire a GC to do the work.

There is no scenario in which taking down a wall does not count as a significant remodel, even if you are retaining some of the existing kitchen elements. Do you have enough construction knowledge to know whether the wall in question is load-bearing? If you don't, don't even contemplate doing this yourselves. Taking out a wall will require patching or replacing flooring. Is there electrical in the wall? Plumbing or other utilities? Do you know? Do you know what building codes apply? Are you planning to get a permit?

It is certainly possible for homeowners to act as their own general contractor and coordinate tradespeople for specific elements of the work. But it is a lot of work and it takes knowledge and experience to do well. Inexperienced DIYers make mistakes like putting refrigerators too close to a wall so that the door won't open fully. Or you can't open the drawers in the corner because they run into the hardware of the drawer that's at 90 degrees. An experienced kitchen designer can avoid some of that, but other stuff is contractor specific. If you make mistakes, fixing them could eat up any savings you gain from acting as your own GC. 

I know the perfect person for your project. I highly recommend Marco Florian, he has great skills on everything related to construction (carpentry, panting, tiling, plumbing, etc). He has done numerous jobs in our home including remodeling our kitchen and two bathrooms. The kitchen remodel involved tearing down a wall and building an island. Marco always goes the extra mile to make sure his customers are satisfied and his rates are very reasonable. He is very creative, reliable, polite, good nature man. You can reach Marco at 510-301-5629 or marco.a.florian [at] gmail.com (marco[dot]a[dot]florian[at]gmail[dot]com)

You can save money by not hiring a General Contractor. It may be worth it if you have some general knowledge if building. If not, it can be a difficult proposition. The General Contractor usually knows how long each job or phase will last and can schedule in advance. They can also figure things out when surprises arise. It will probably take longer if you hire the sub-contractors yourself. You may want to check references on each one. But you might also have more control over outcomes. Even though it is not a full remodel, taking down a wall is a significant endeavor involving structural elements that support your home. Don't underestimate the work involved.  Contractors can usually get a discount on supplies, so buying materials yourself might not be best. Good luck!

We did this about 10 years ago and were very happy with the outcome. It cost about half what we were being quoted at the time to have a general contractor do it, but it definitely required schedule flexibility, and we did not yet have children--not sure I would do it with small kids underfoot. We learned a great deal about the remodeling process (including navigating city permitting, which has served us well in the years since then!) We did the design ourselves and then hired a kitchen designer on an hourly basis to review the plan and give feedback on things to consider doing differently. It was exhausting but fun, and some of the contractors we met in the process have come back to do other projects for us over the years.