There are a few rennaisance based RPGs already you can look at for ideas. Maelstrom was one I had in paperback, it had some nice ideas in it. Low fantasy sort of thing with magicians etc feared and persecuted.
I'd also recommend look at some of the innovations in current RPGs like D&D 5e for ways they streamlined gameplay. D&D 5e has "advantage" and "disadvantage" rather than plusses and minuses to rolls. if you have advantage: 1 in a situation, you roll two dice and discard the lowest, "disadvantage:1" you roll 2, discard the highest. Same general effect as plusses and minuses to rolls but much faster to resolve.
This could be extended to a skill system. Normally, you'd have skill percentages, rolling against the skill, then adding or subtracting modifiers to that roll, then comparing to a target value. Here's a nice idea based on some of the 5e ideas. Roll all action checks against an attribute. If the target difficulty is 0, then you just do the raw roll and succeed on attribute or lower. For each difficulty level above 0, you roll that number of extra dice and take the highest roll. Add a skill point system to that, and you subtract your skill from the difficulty. If total difficulty is now below zero, you roll the extra dice but take the lowest rolls. Probably for sanity's sake set it up so that you never need to roll more than three dice. Probably limit skill points per skill to e.g. 6 points, and you gain 1 skill point to spend per level. So a level 20 character could max out 3 skills.