Like you, I'm teaching myself Irish and I take any free time to write down something in a notebook in Irish. For me, it's usually just any one thought or two that comes to mind, which I think is a good exercise. Whether it's simply "I'm going out today" or silly, like "Oh no, my coffee is cold!" or even describing the outfit I'm wearing. My advice would be don't put too much pressure on yourself to write a journal entry that's as detailed as one you might write in English; and don't put too much pressure on yourself to get it perfect. Write any thought at all (even just one), and if you're unsure of your sentence form, do what you can and look up on it later. That's what I do. Sometimes I get it horribly wrong --with grammar and/or spelling-- but that's not a bad thing; because I looked it up right away, I was able correct myself. Let yourself make mistakes (even wild guesses) and then look them up after that to see if it's formed properly so you can correct it if it's not. You might have gotten it right; or you might have found that you made such a silly mistake that even you can laugh about it! You didn't start out speaking fluent, grammatically correct English, right? You made mistakes very early on, but you were corrected along the way and now your communication is perfect. 
EireFirst.com has lessons and information on verb forms, sentence structure, and the nature of masculine and feminine nouns which has certainly helped me. The lessons are written out in very clean, organized paragraphs and tables. I like to print out the lessons and put them in a binder to study, teaming them up with my Talk Irish sound files on my iPod. I owe a lot of my sentence structure knowledge to this fabbity fab website as well. I download all of the Focal an Lae and then edit the Properties of each file, separating them into Albums (subjects) and adding the sentences into the "Lyrics" section of the Summary (I can explain this in screen shots if you like). Then I add them to my iPod where they are organized by their Album name (Around the House, Seasons, Holidays, etc.). When I play them on my iPod, I click the center button 3 times to view the "lyrics" so I can see the Irish as it's spoken and the English translation. Actually studying the set up of Irish sentences provided can give you the idea of how to form sentences on your own. I personally looked for patterns and analyzed the sentences, and then I searched for confirmation on my "discoveries" afterward. I really do recommend EireFirst.com, but please don't overwhelm yourself with several lessons at a time! I print out a lesson and study it. When I feel I've already grasped it enough (whether it be 3 days or 3 weeks), I print out the next lesson, but I keep every single one to refer back to later should I forget or become unsure of something.
You say you're afraid to branch out using the forms that you're given as examples in your Irish book. Why is that? That's what they're for! 
Those sentences are given to you to show you how to convey that kind of statement. I think all you need is more self-confidence and less pressure on yourself. Don't be afraid to experiment and have fun practicing those forms. Use the examples as a template, and replace the words with others.
For instance, the Talk Irish example sentence:
"Cuir an sceanra ar an tábla."
Put the cutlery on the table.
Try changing the subject, from cutlery to a pen:
"Cuir an peann ar an tábla."
Put the pen on the table.
Now try changing the last noun, from a table to a book:
"Cuir an peann ar an leabhar."
Put the pen on the book.
Let's change the verb now, from "put" to "throw":
"Caith an peann ar an leabhar."
Throw the pen on the book.
Yes, it's a pointless statement (haha, why throw a pen on a book?) but that's an example of how easy it is to form your own sentence when given a simple example. 
Watching Aifric on the TG4 website has also helped my Irish tremendously with vocabulary, grammar, and sentence structure. It's a comedy teen programme so it's easy to pay attention to and the episodes are short so it's not too overwhelming. I believe it's in Connacht dialect, and I'm learning Ulster on Talk Irish, but it isn't difficult for me to understand their actual speech (not talking about the subtitles here) when they're saying something I already know (it's like how I speak with a New York accent, but I can understand someone from Boston). If I hear a word I recognize, I will even rewind the scene over and over to hear how the word or phrase is used in the sentence if I'm not too familiar with the real usage. I always have http://www.irishdictionary.ie/dictionary up at the same time to look up any words I'm curious about that I don't recognize (using English to Irish). I don't look up every single word I don't know, because that would be very overwhelming.
I would love to help with sentence structure and verb usage. 
I am a grammar geek when it comes to English, and I have found that I am not that different with learning Irish grammar and sentence structure. I've found that Irish sentence structure itself really is not as difficult or unpredictable as it looks at first and I found it is not as different from English as most people say it is (yes, it is different, but it's not impossible). You really have to let yourself make mistakes and not be afraid to take chances so you can grow. You won't get into any bad habits as long as you correct yourself right away; you seem to really care about how well you do. If you'd like someone to buddy up/learn with, you can private message me any time. I would love to share my findings with another self-taught learner, especially verb usage. I've been studying consistently for about the same amount of time as you have (5 or 6 months and about 3 years very inconsistently before that) and I've really become passionate about it.
*I edited this post after I reread your post and saw that you had the resources to see examples of sentences, so I crossed out my input so you could read it but ignore it (so sorry about that!). Then I wrote the paragraph of examples. >.<