Welcome :)
Scratch built kits nowadays are very precise compared to many moons ago, don't be put off because its your first build or worried, just take your time with it & enjoy it, also remember you got the net as a massive reference during your build where you can pull up pics/videos & even build logs if your lucky of someone else who has built the same model etc so you won't be going in blind as they say. I'm part way through my 1/12 scratch build TUG, no kit. no instructions etc its purely scratch built from plans I have & this is also my very first build! (my build log is in my sig at bottom of this post), At the start some said things like "start off with a small kit first etc" but you know yourself what your limits are, over the years I've built numerous model kits (not RC just small static models) but this helps when i'm now building my TID Tug, so don't let anyone put you off just because its your first build. Like i say, you know yourself what your limits are, no one else does, sure they can advise & that's what it is, just some advice, i've seen a few topics where someone has asked similar questions (not on this forum but others) & the *newbie* decided to against advice of so called "elitists" & start a scratch build, needless to say the elitist chaps got the hump because the newbie didn't take there advice! but the newbies build ended up a great model etc.
So my advice, go for a kit, not only is it fun, but when you first put her to water you will feel great knowing that you built it up from pretty much nothing & now she sails! I did my 1st water test with my TID the other day & i was chuffed to bits, still a long way to go with the build but i was very happy with what ive accomplished so far :) Just remember though that with kit building, you will need all the tools/materials & this can add up in terms of £££. If you think you will be building more in future then any tools you buy for your 1st build won't be wasted money, but if you think this will be the only build your going to do, then maybe ask around friends/family to borrow some tools etc instead of buying them
As for converting static models to RC, this can be a whole new ball game! ..sure it can be done, but can also be very tricky depending on the size of the model & the way its been built, they usually require quite heavy modifications, my advice on this as your first build is to avoid & get a kit that's designed for RC!