Je n’en ai peut-être pas l’air comme ça mais je suis un …

In this sentence “comme ça” means “at first sight” or any other similar term. It means that we couldn’t expect that from you without knowing you a bit. For instance “Je n’ai pas l’air timide comme ça, mais en fait j’ai beaucoup de mal à parler aux gens” could be translated as “I know I don’t seem shy but I have a lot of trouble talking to people”.

Je n’en ai peut-être pas l’air tant que ça mais je suis un …
There, “tant que ça / plus que ça” are synonyms and mean “not … all that much”.

Note : “pas l’air plus que ça” and “pas plus l’air que ça” are the same and the words can be put in any of the 2 orders. The second one seems more correct to me but the first one is more used in real life.