@Sacel
1, 3, 4,
You don't put a baby to sleep on the belly until it is able to turn from supine to prone position. It's one of the 3 take home advice given to parents for SIDS prevention here in Northern Europe. No smoking and temperature monitoring (baby should not be sweating) are the other 2. There are exceptions to this, NICU procedures f.inst. - but take home advice for parents are as stated. Same goes for smoking outside - particles are stuck in the clothes (also if you cannot 'smell them'). Don't smoke around babies, period.
2) The kidneys of babies <4mo are not mature enough to excrete excess proteins, minerals, electrolytes etc. Feeding your baby solids before, on average, 4 months puts tremendous stress on the not yet fully developed renal filtration system. This causes buildup of urea etc, and it is harmful to your baby's health. Don't do it!
Babies should primarily be feed breastmilk, or formula, pref til they're 6 mo. Gradually switch to a combination of breastmilk/formula and solids from 4/6 mo until 12 mo, as breastmilk/formula alone is not enough at this point. After 12 mo the immunological benefits of breastmilk declines substantially (IgG etc), but if you can and have the option of breastfeeding it's well worth it as a supplement to solids for the nutritional value alone. At 18 mo they should eat what you eat, micro bites and nothing too solid as to avoid choking, naturally.
5) I've seen no evidence of the benefit of this. Babies do not yet have 'intent'. Frontal cortex is barely even worth mentioning here, really. Attaching manipulative intent beyond basal needs to a baby's crying is stupid. If they cry there's usually a good reason - even if one cannot identify it immediately. I'd never leave a baby crying for hours. Never, ever.
6) Yeah, this can be hazardous, choking wise. Don't get too hooked up on the numbers or sizes vs age though. The rule of thumb is, that the flow has to follow your baby, not the other way around. If the baby chokes and spits up a lot, the flow is too great - decrease the size. This is assuming your child is healthy. Contrast: you can feed newborns fine with a 2cl cup if they are having problems suckling.
7) Babies need diaper changes often - every 1-4 hours for the first couple of months. There is nothing like a red or wet bottom that makes a baby cry and generally uncomfortable. I'd change diapers as often as possible here - don't be cheap. You'll regret it a million times over.
8) You're caught up in numbers and the desire for schedule. The regime is this: Your baby cannot go hungry - feed it as often as it needs. Always. There is no such thing as an unnecessary 'snack'. Your baby needs building blocks to grow - and hypoglycemia is a threat. Holding back here is not an option. The hunger signals is what you have to be good at: early stage signals such as rapid eye movement, suckling motions, leg and arm movements, hands to mouth. Later: unrest, grizzle, intermittent crying, and (too) late stage: relentless crying, body movement and redness of face. Food. Now.
That being said, in a grander perspective it's beneficial to have grandparent-child relations - especially later on when you want a nap, need new baby clothes, or a shoulder to cry on. Don't alienate your family completely
