There's an article on Ireland Reaching Out website which mentions amounts given at baptisms. It's in "News" section. https://irelandxo.com
Typical amounts were in shillings not pounds except for families who were comfortably off.
Title of article is "Irish Naming and Baptism Traditions". It's currently on page 7 in the "News" section.
https://irelandxo.com/ireland-xo/news/irelandxo-insight-naming-and-baptism-traditionsTo summarise relevant bits in answer to some of your questions:
Before the Great Famine:
A typical bride was in her teens. She might have 14+ pregnancies. Baptism window was 28 years. Babies might arrive annually during first 5 years of the marriage. Gaps between births would increase in later years of a marriage.
After the Great Famine:
Typical bride was aged around 20. Baptism window 25 years. Births might be around 2 years apart with longer gaps later in marriage.
"The stipend":
2/6 (2 shillings and sixpence or half-a-crown) was typical for a small farmer in West of Ireland. A wealthier man might give £1.10 ( £1 and 10 shillings) in a good year. A stipend 0/0 = poor.
(It doesn't say when.)
I looked at my families' parishes. Ancestors were small farmers. Stipends weren't noted in one parish baptism register or the column on page-edge has worn away. Most people paid 3 shillings in the other parish in 1850's & 1860's. (Pages for 1840's are tatty and not easy to read.) A few paid 2/6. Some people in town (Castlebar), perhaps shopkeepers, business owners, gave amounts between 5 and 10 shillings. Some salaried fathers, e.g. army sergeant, hospital sergeant (?), superintendent (?) gave 5 to 10 shillings. There were occasional £1 donations. 2 solicitors, one described as "Crown solicitor" each paid £2. The archdeacon baptised babies of some better-off people. No stipend for most baptisms noted "illegitimate". I noticed 2 sets of twins, 3/0 for each pair. (Baptism BOGOF?)
At those rates my ancestor got his half-dozen children done for less than £1 in total.
