it's been a hot minute since i've really skinned proboards, so i won't speak for it - i personally find it a nightmare to skin for by this point, but that's because i find it very messy to work with for how i prefer to go through the skinning process, but i know a lot of newer coders prefer it because it has options beyond just throwing you into the deep end with the wrappers + template layouts + css, so your mileage may vary.

but what i can speak for is jcink - which in my opinion, if you can successfully edit and manipulate a premade on jcink, you can almost definitely skin for it. granted, you might not be able to produce something with all the super fancy bells and whistles that you might see on some of the higher-end skins (like the varying board layouts or running animations or the like) but you should be able to produce something functional and clean, which is what's more important than all that fancy stuff anyway.

i've been skinning jcink for four years now, give or take, although i guess you could say i've been skinning for longer since i've done a lot of heavier-end coding edits for the skins i use (to the tune of "completely ripping out mini-profiles or headers to redesign them from scratch to better suit my needs") for closer to six or so, both on proboards or jcink. i personally don't find skinning to be too much more difficult than coding a template or those smaller portions of a skin, but then i also don't tend to do things that require me to have to do much with javascript.

my personal process for skinning is to basically design the entire layout on codepen first - header, footer, board layout, info center, thread layout, member list, post layout with mini-profile, profile layout. all the big stuff. when i know what i'm doing design-wise, i've managed to pull together a skin in a week or two, but i've also taken more than a month on a given skin; in either scenario, it's probably about 70+ hours of work just to get that first step done. but the flip side of that is that it's honestly pretty easy to convert it from that raw codepen into the actual site skin since jcink's very transparent about their variables for the html templates (basically all the individual layout things like boards + threads + posts + profiles + mini-profiles) and the wrapper (header + footer + anything else static in the design like a sidebar). there's a few things you learn how to do via workarounds or that are missing (like the <% SUBACCOUNTS %> variable for the dropdown or how to add avatars to the thread layout or everything with the macros) but it's not that much. for me, an entirely finished skin is probably about 80-90 hours' worth of work between the initial codepen design, converting it over, and then doing all the little on-site tweaks like redesigning the post buttons and all that.

my best advice for "i can't skin and i don't know how" is honestly to just..... start messing around with the premade skins. because you'll learn more actually working with the variables and seeing how people did xyz thing than you will just. generally brushing up on stuff. (well. that and learning how to do if/else statements from jquery since i use those a lot in skinning and i remember jquery was basically a staple for proboards). feedback is probably more gonna be hit or miss just because like..... design is hard, i probably only like the designs of half the skins i've made in those four years i've been actively doing it. but you're also not going to really get better at it short of doing it and learning what works well and what doesn't so uh. yeah.

i'd also recommend getting p familiar with caution to the wind if you intend to go with jcink - the site is more of a rl community but they've been around for actual years so they have a really big library of coding resources, which is nice for things like a highlightable code box or a toggleable cbox or the like. (they also have a lot of jcink coders there, so it's not a bad place to go for coding help for if something breaks or you reach a dead end.)