1.画画 and 画画儿 do not have any differences in actual meanings.For example, 他在画画=他在画画儿=He is painting. However 画画儿 is usually more casual and informal, and often used in oral Chinese and Chinese northern dialects. Especially when a modal word like 呢 is at the end of a sentence, we often use 画画儿 instead of 画画. For example, 他画画呢 is so much common than 他画画 in oral language, both of which mean he is painting.
2.吃 is completely a verb meaning the action of eating. You can use 吃 + any nouns to express sb. eats sth.. Like, 吃糖meaens eating candies, 吃肉means eating meat.But 吃饭 can be used both as a verb and a noun. For example, 吃饭对人来说是必要的。=It is necessary for human beings to eat. 我在吃饭=I am eating meals=I am eating.Plus, when you say 吃饭,the things you eat can only be meals.
3.Yeah, both 游泳 and 跑步 can be used as a verb and a noun. For instance, 他在游泳/跑步=He is swimming /running 游泳/跑步对你的身体有好处=Swimming /Running is good for your health.
4.Yeah, 蚂 is a polyphone. 蚂(mā)螂=蜻蜓=dragonfly, 蚂(mǎ)蚁 =ant, 蚂(mà)蚱=grasshopper. However, commonlly we do not call 蜻蜓(dragonfly) as 蚂螂.
5. Just for your information, when I learned English in the past, my teacher told me boring is used to describe the thing which gives you the feeling of boredom while bored is used to decribe the feeling itself. So on the one hand, 无聊 is often used to describe a thing and 闷 is often used on humans. On the other hand, when 无聊 is used on humans, it means you have nothing to do or not an interesing person to get along with. For example, 我现在很无聊 means I have nothing to do right now. 他是个无聊的人=It is boring to get on with him. And when 闷 is used on things, which is often weather, it means hot and humid. For example. 这天真闷。=It is hot and humid.
Wow, so many words I have typed! Hope the above can help~
p.s Oh, by the way, generally we do not use 非常谢谢,非常感谢 and 太谢谢了 are much better :)