Typically lawyers are only recommended in complicated cases where you'd need someone with extensive knowledge of loopholes to help you get through. The paperwork is fairly straightforward and you guys could easily complete it on your own. Just pay attention to details and double and triple check everything. Having said that... as C/Trini mentioned, you can get a lawyer or consultant to look over your application for you (this is different from having them represent you). Some people have issues with lawyers/consultants, but I strongly recommend getting the review. If nothing else, it gives you peace of mind knowing that someone very experienced reviewed your file and feels confident in your submission. Our consultant reviewed our application package and said we practically didn't need him BUT...he did give us two pointers I know for a fact saved us delays later on, so it was well worth the $250!
You mentioned going to the US as a minor and being without status now. The fact that you went as a minor (I assume as well you have family who brought you there) bodes well for your case, so be sure to highlight this in your cover letter. Since you were a minor, the decision to remain without status wasn't yours and therefore cannot be held against your character. While immigration status is not itself grounds for denying spousal PR, the VO's job is to judge your relationship and your intentions, so essentially they are making judgments on your character and you want to do everything to paint yourself in the best possible light. So anything that makes you look good...use it to your advantage! Also, in the US undocumented people are termed "illegal", but be careful of the words you use on your application. If you entered legally (i.e. on a visa of some sort) you are NOT illegal, simply "out of status". The term "illegal" generally implies that you entered illegally (i.e. using fraudulent documents or none at all), so no point in potentially creating that mix-up unnecessarily!
Another way being brought there are as a minor helps your case is that by now you're somewhat comfortable/established in the US, so if your intentions were to marry for immigration status, it would obviously be much easier to just marry an American. The fact that you're marrying someone elsewhere and leaving a comparable lifestyle helps prove your relationship as genuine (you don't have to state this in your application, just letting you know how the VO will see it).
Good luck, let me know if you have any more questions
