Honestly, start with web design and branch out into SEO/Programming/scripting.
Would be my recommendation, too. SEO isn't that easy if you don't want to rely on things that could get your clients penalized like PBNs and similar. For own sites, other story, but for clients, SEO is a lot different from what you are often finding and reading here. Most of it is knowing people and people who know people. You need a good network, other agencies, publishers, etc. That's nothing technical you can learn, that's something you have to grow over time.
In addition, web design is a great way to make a client "your" client long term. Most small to medium "brick & mortar" style companies look for a all in one solution. Someone who builds the website, maintains hosting and the website, updates it if needed...and does SEO as well. Especially basic local SEO is a great way to start, competition isn't fierce, you can rank well without too much effort. Works like a clockwork, no fancy or really creative approaches needed. Being this one partner can be very profitable, one time charge for the website, plus a long term (or short term auto-renewal) service contract that includes maintenance, updates and SEO. This type of customer is very loyal and stay forever if they are happy with the overall package and results, they don't expect some shiny pitch, deals are made during a nice meal.
Later, you can expand the SEO branch steadily. Important: If you buy some links here, you'll rarely get a report. That's different in the "real" SEO world, because there are so many ripoff SEO companies, transparancy is a must have for trust. Clients expect some sort of proof or work, what was done, why was it done and how do rankings and traffic develope.
