If you are low on startup funds, you should focus more on production marketing first. Then trademark down the line when you can afford to put some money towards legal stuff.
To be eligible for trademark, your logo or brand name needs to be used in way that identifies the source of your goods or services. Simply using it on t-shirts or flyers won't be eligible. Using on a website may be ok, but it depends on how it is specifically being used. For an apparel trademark, you should be using the brand name or logo on a neck label or hangtag.
Part of the trademark registration process is to prove that you are using the mark in commerce. So you need to be using the mark first before you can trademark it. You can file your trademark with an "intent to use," meaning you can start the process before you are using the mark. But the process cannot be completed until after you can prove you are using the mark.
Registering a trademark won't automatically prevent someone from stealing your logo. So you are correct... You will still have to go to court - and pay legal fees- to protect your trademark.
You can make a public claim to your brand name or logo by using the ™ symbol next to it. This offers a small level of protection known as "common law trademark."
But trademark (whether registered or common law) only protects the brand name or logo. It does not protect any of your designs. The designs are separate and can be protected under copyright.
