Hello and welcome. Settling on wearing 24/7 is a big decision. You seem to be aware that it can result in changes to the way your body works, and that your individual response to diaper re-acclimation may be rather strong, so I won't belabor it. Plenty of discussion has happened around here about it. Just be aware of your body, know your limits, and don't hurt yourself.
I'm about to say a lot, but getting used to 24/7 boils down to getting back into diapers and staying in diapers. It's obvious, but that's the simplest way to say it. The rest logically follows from the knowledge that once your current diaper is done, you are absolutely 100% going to be putting another one on.
You will have to get used to carrying a diaper bag when out of the house with at least two changes in it. I use a backpack that isn't going to look out of place where I go. This one can be a big change for many people who don't tend to carry relatively big bags with themselves everywhere. It's also obvious to anybody who knows you and can draw questions. Make sure you're prepared for that. Also a lot of places do security/loss prevention bag checks these days. Make sure you're mentally prepared for that too.
Get comfortable with using diaper creams or other skin protectants. You might not need them all the time, but you will want to have some handy to help heal and prevent rashes.
On that note, don't sit in soaked diapers too long and, if you decide to mess, definitely don't sit in messy and wet diapers too long. The combination is particularly hard on skin. Consider finding a changing schedule that works well for your daily use where you change more often than might be necessary, and stick with it. Remember, even if your diaper only absorbed one bladder full, it still did its job...
Maintain a good hygiene routine. Remember that diapers are at their core a sanitary tool. They're to keep you and the environment around you clean and happy. That means you also can't slack off keeping yourself clean! Don't neglect cleaning your diaper area. Pay extra special attention to it when you take your (regular) bath or shower and clean thoroughly with wipes each time you change. You will go through a LOT of wipes so buy in bulk. I like Costco's Kirkland brand wipes.
Changing outside the home is mostly a head game. If you have a well packed diaper bag and are practiced, it's straightforward but the nerves of it are something you have to get over. Opt for private single serve restrooms if you can, obviously, but if you don't have any available, you just have to do the best you can with what you have. If you're used to changing while laying down, get comfortable with doing it standing.
Get ready to say something in defense of your diaper wearing (or, deflect suspicion) to literally anyone who interacts with you closely in your life. The approach is up to you, and most often people don't pry about potentially medical stuff, but sometimes they do.
Find clothes that maximize diaper discreetness and fit well over your new underwear choice. You may want to shop for some new clothes (with a diaper on, of course). Understand that certain clothing choices are going to potentially give you more grief than they're worth, and make it a challenge to be stealth wearing. Recognize that save for a special few, precious articles of clothing, adult fashion is not designed with diapers in mind.
Because the end result is the same (dirty diapers), you should feel free to choose to use your diapers in whatever manner you want. However, maximizing the conveniences of diapered life demands that you be comfortable using wherever and whenever. People generally have some level of bladder shyness in certain circumstances (in bed, in a car, laying down, etc). You can choose to train and try to get past those situations or not.
Diapered overnights are a special beast. You may want to get an extra heavy absorbency diaper or boosters for your usual for nighttime. You can sleep without extra leak protection and your diaper will work just fine (usually), especially if you wet lightly. But any heavier and you will have to deal with leaks eventually.
All diapers are cheaper per unit in bulk. Buy big.
Never be afraid to take a break if you need it! You are choosing to wear constantly. That means you have the ability to stop. Do it if you want to or need to. You are still 24/7. No one is keeping score but you.
Diaper free air-out time is important and fun. Make sure to include some in your daily routine.
There are obviously more things to consider, but these are the first things to come to my brain right now.
As far as messing your diaper is concerned, a lot about it is really your choice. Some people love it, some people hate it. Almost everybody finds the cleanup to be trying at times, although sometimes it's easy. The way I approach it is that I think diapers should be used for both wetting and messing, but I only mess under controlled circumstances, when I won't be irresponsible and when I can clean myself promptly and thoroughly.
Most diapers have at least second-chance tapes so you can take off a diaper to use the toilet for #2 and put the diaper back on to wet, if you don't want to mess in your diaper. Hook and loop disposables, modern cloth, and pull-ups are the easiest in that regard, but a lot of adhesive-tape disposables are fine with this as well.
If you do want to mess, then it's about just relaxing when you feel the need and the time is right. It should be natural. Don't push hard. Hope that you get lucky and it's both easy to get out and easy to clean up from. The more you move afterward, the more you smell. Make it a priority to change very soon.
Make sure you have a lot of wipes available at change time, as well as nitrile gloves. Use the padding of the diaper to get most of the cleanup work done, then switch over to wipes. Shake the poop out into a toilet. Be super generous with cleanup and get yourself squeaky clean. Consider showering afterward if you are at home and feel like you need it.
