Hi Maija, this is a wonderful initiative! I'll start with some points from my experience as a long time wearer of chastity belts and eventually extra gear.
Chastity belt and hygiene:
If possible, removal 2x / day with the possibility to wash / shower your private parts and cleaning the belt. Put the belt sometimes in the dish washer. Alternatively, taking a bath helps to keep also the belt clean if your partner sees no possibility to remove the belt.
For toilet, first to say I wear a chain based belt. The "big" one is no issue, peeing, however, more. We have a comfortable BD at home including air drying, which helps a lot. Out of my home, I try to hold it, if possible. But I also frequently wear incontinence pull-ups (at least in the colder seasons, nut during hoot summer). Not for peeing, but to hold drops afterwards. So lots of toilet paper and then pull it up and change as soon as possible when at home. For me, all this stuff with syringes is not so useful.
During my period, I put thin rectangular inserts like the Abena Abri-Let under my secondary shield. They are meant as boosters for diapers or pads for women in childbed. The benefit is, that they contain no foil and glue, so they slip quiet easily under the shield. Together with a pull-up, I fell secure during my special days.
Hiding the belt:
Bodysuits prevent a naked back and the waistband from peeking out, plus dresses/skirts, emphasising the waist, but more A-line at the hips. Add a wide leather belt.
Hiding thigh bands (I wear them occasionally):
Dress/skirts as above. Bodysuits as above. Stay-up's with higher DEN in longer versions nearly to the hips keep legs warm, prevent rubbing of the metal hoops. In winter I may also put on cycling shorts/bodice trousers with long legs before the thigh bands are put on. Together with pull-ups and stay-ups and a skirt made of thicker fabric and/or a underskirt, I haven't really gotten cold yet. A silicone tube over the chain prevents suspicious noises.
Chastity Bra (I wear it occasionally):
I see the biggest problem in the varying size of your breasts (I have C cup, with additional metal almost D cup). This may be noticed by others you meet regularly. Especially women have a good eye for that. My husband likes more tits anyway. Therefore, I regularly wear padded bras or one bra size bigger and some booster inside, also in bodysuits without distinct cup. When wearing a chastity bra, I put something on top which distracts from telltale imprints of the metal. Either high-waisted bodysuits or a normal bra (then without padding). I fix the straps with 2-3 thin velcro strips over the straps of the metal bra. Then nothing will stand out, even with blouses and pullovers that are not too body-hugging. But you definitely don't have to wear bags!