Do you think that getting married at 20 with little financial support amounts to messing up your life?
Define "little financial support".
If you marry, you are likely to have children. You have to consummate your marriage and it is unhealthy in your early 20s to not be having sex at least several times per month for most couples, most of the time. People should not be having 3 children by 25 and then a Josephite marriage until their wife hits the menopause because they genuinely cannot afford a larger family. That is unnatural and unhealthy in 99.9 percent of circuмstances. It is likely to lead to all sorts of problems which will either give you an unhappy marriage or a broken marriage. Those two outcomes are messing up your life.
So children will come along at about the rate of one every two years in your 20s and one every 3 years in your 30s.
So, if at 20 you are qualified as a lawyer or an ambulance driver or medical technician and have debts that need to be paid then no. It is a reasonable risk to take. Over the next five years you are likely to be able to pay those debts and have enough to support a fast growing family.
You don't need luxuries, but you do need things like a home, the financial capacity to pay the rent or mortgage, a car to move little babies and young children around. Public transport is not really feasible unless you live in the middle of a major metropolis.
You also have to consider your family situation. Would or COULD your inlaws or parents of a wealthy brother or sister come to your aid if you were going to be evicted from your home? Do you live in a welfare state that has a safety net? What would living at that safety net level be like?
How entrepreneurial and flexible with what work you would do are you? How good are you at selling yourself into a new job are you? Could you walk into a taxi firm and convince the boss to give you a try and then become his most relible driver? Could you be a taxi driver and work the hardest shifts that pay the best rates? Are you a sensitive and/or over scrupulous person that would have a problem picking up a hooker at 2am and driving her, too or from, what you imagined was probably work? Taxi drivers have to do this sort of stuff. It's not purely drive white middle class churchgoers around. What would you do when he called you in a desperate state and asked you to drive on Sunday?
There are cheaper and more expensive places to live. There are places with better options for getting to Mass. But if you move to Texas because it is cheaper, and have no extended family support then who comes over to help your wife when she has three children under five or one that is severely mentally handicapped. Your mother in law can only help if she is within travelling distance. Does your girlfriend's family appear willing and ready to help?
In short, your question is badly thought through. Nothing amounts to messing up your life because we don't know the future. There are known risks and unknown risks. There are unknown risks you know you don't know and there are unknown risks that you have not even thought about.
If you go hiking in the Klondike and take a small back-pack and a bar of Chocolate, a print out from Google maps and a compass you got in a Christmas cracker are you being prudent? Probably no, but it would depend on other factors. If you are Ray Mears or Bear Grills, then probably it is OK. If you are some idealistic fool like that kid in the movie Into the Wild who finds an abandonned bus in Alaska and dies there then you are stupid.
The answer therefore is to think about it, ask the experience of married people you know and trust, find out what degree of support they had from inlaws etc. Consider the nature of the woman you are marrying and how poor she is likely to consider "too poor". Most Trad women would put up with a 10 year old reliable and respectable car, maintained by you but they won't want to eat rice for a week because your family car needs a new clutch or engine replacement. They won't want their children looking shabby and have people look down at them for being poor and having too many children and due to the nature of Traditionalism and being split up it is unlikely that all your family friends will be Traditional Catholics. In short one financial crisis every ten years is acceptable, but lurching from one crisis to the next or asking her to wash clothes by hand or walk 2 miles to the laundrette every time the washing machine breaks and you cannot afford to have it repaired till the Pay Day after next, because your clutch needs fixing is taking an unacceptably high risk of your marriage being an unhappy one. In my experience, women tend to respect their husband for being a good father to their children, (playing, entertaining, disciplining them), providing financial support (bringing home the bacon) and being faithful and loyal to them and them only.
So there is no simple answer. It depends a lot on who you marry and many other factors, only some of which are mentioned above. It also depends on who you are, how street smart you are, how prudent you are, how mentally well balanced you are. The long and the short of it, is if you marry a middle class white trad girl who has grown up in a safe white neighbourhood then almost certainly she is going to want the same thing for her family. You will have to compete for housing, groceries and utilities with contracepting couples, ɧoɱosɛҳųαƖs, singletons while having far more than the average number of children. To take a low risk path, that will require you to out earn the average person, or, find a wife that is content being much poorer than she was growing up.