When assigning ability scores, feel free to use the Point Cost table on page 13 of the Player’s Handbook. You have 27 points to spend on buying your Strength, Dexterity, and so on. You can roll if you want.
Feats (PH 165-170) will be allowed. Encumbrance (PH 176) won’t be strictly enforced because I hate excessive bookkeeping, but (if and when I remember) every now and then I’ll check in to make sure nobody’s lugging around 400 pounds of gear. Lifestyle (PH 157-158) may or may not be used in the future, depending on how the campaign goes. For now, as you’re exploring on the open seas, it isn’t very relevant.
Any creature with a racial intelligence of 9 or higher is 1) freed from racial alignments, and 2) able to practice a Class (e.g. Fighter, Wizard, and so on). See Monsters With Classes (DMG 283). If you’re sentient and intelligent you most definitely don’t have to behave the same way as your fellow creatures, although many will.
Religious cults don’t have to (but sometimes do) use holy symbols, and such symbols are not necessary to cast divine magic. Nobody really knows how magic works and if there really is a divine presence.
Components aren’t necessary to cast spells, but using the listed components might provide an Advantage when casting. If you want to put in the work you can get something out of it. However, spells with a verbal component must be cast out loud (as this has gameplay ramifications). Also, GP requirements for spells remain in effect (this is an important balancing feature, although I don’t think any spells below 3rd level have a GP requirement).
Initiative is changed so that your Dex modifier is doubled (so a 0 vs. +3) are swamped by the randomness of the roll. Under the house rule, it’s a +0 vs. +6.
Most trade in most of the world is exactly that: trade in goods. “I’ll give you this axe for two goats.” Therefore, the most desired currencies are not coins but commodities. Salt, furs, spices, ivory, linen and wine are all examples of trade goods that will be more desirable to more people than gold.
The great majority of people have an effective gross income of between 10 to 50 gp per month, paid mostly in goods and services, with laborers and trade apprentices on the low end and skilled artisans at the top.
Many spell books are more than mere collections of spells. They may also contain valuable research data, expressed as a chance that an answer to an occult question might be found in the text and marginalia. For example, a spell book may have a chance of describing the origin of a certain magical item or the properties of a particular creature. On a successful Intelligence (Arcana) ability check, and 1d6 hours of study, the desired information might be found. The DC is based on the obscurity of information researched versus the specialization of the text. For example, a book about the Outer Planes could contain powerful summoning spells, but also useful information on fiends and Abyssal politics. It is much less likely to contain information related to gnomish illusions.
Spell books are written in the same variety of languages as are other books, though they may in addition be magically encrypted. The same spell book may be found in different translations and editions, some better or more complete than others, expressed as a bonus to ability checks for particular topics.
Changes to weapon damage or properties (PH 149):
Weapon Damage Properties
Halberd 1d10 slashing Heavy, reach, two-handed, tripping
Whip 1d4 slashing Finesse, reach, tripping
Reach weapons may be used through a space occupied by a friendly combatant.
Slings and thrown weapons may add the attacker’s Strength modifier to their damage.
Tripping weapons are able to trip up opponents. Attackers may opt to trip an opponent instead of inflicting damage; if such an attack hits, the defender must make either a Strength or Dexterity save (target’s choice) versus [10 + the attacker’s proficiency bonus] or fall Prone (PH 190).