There is no right size; it's most important to include key word phrases that have a realistic number of searches and level of difficulty that's achievable. When search terms are too broad, you'll have no chance of a high page rank.

You want to make sure that those keyword phrases are used in on-page SEO (landing pages, web pages, calls to action) and off-page SEO (social media). Then you want to maximize effectiveness by focusing the keywords on landing pages that are highly targeted and have a call to action for the visitor.

Since I'm not sure what you do, I'll give you an example from our own world. Among other services, we provide CRM services and sell CRM software. The keyword CRM gets search 39,000 times a month and has a high degree of difficulty because it's so broad. So while that broadly describes what we're about, it's useless as a keyword.

However, if we choose what's called a long-tailed keyword, more targeted to what we do, such as CRM implementation (130 searches per month), CRM solution provider (220 searches per month) or CRM features (43 searches per month) each with a lower degree of difficulty, our likelihood of being found by someone who is looking for what we do goes up exponentially.

So, rather than focus on a number of keywords for the portfolio, consider instead the most useful keyword phrases that help people find YOU and use them in content that resounds for your potential buyers. That said, we've identified about 60 keywords phrases across our business offerings that we tend to focus on, but that number could easily be more or less and still be effective depending on strategy and tactics.

You can use Google analytics to help (look at ad words) or you can use a subscription service such as HubSpot for a full set of tools to put in your SEO toolbox- that's what we do. If you have a few keywords (read that as keyword phrases) you're thinking about, toss them out and I'll be happy to give you some feedback on them.