Just a small space/gap is all you need ...just so you keep as much of your own hair as you can and so the perimeter is not overlapping onto it.....
I`d avoid coloring / thinning the front..that`s really getting into ` deep water` ...as a new wearer you`ll have enough to deal with, without all that. Thinning it out, is very hit-and-miss...the front area is the most visible and it could look totally ` off` if you go ` at it` ... just order the system as normal ---you could ask for a little extra graduation to be included if you feel you need it.....
I usually prep. my system before going to a stylist either by attaching tapes to the base or I simply bring a tube of ` Got2bglued ` spiking glue with me ..this is fast /easy to apply and will hold the thing in place whilst being cut-in....most stylists in ` normal` hair salons don`t want to be fussing around with glues/tapes etc....it`s different if you go to a place where they deal with systems all the time or even sell them [ those ones usually won`t do a cut-in unless you bought a system off them] ... I tape mine with strips of tape, peel all the backing-papers off and fold /crease a few millimeters of each one over ` onto ` itself [to provide a grip-point ] I then ` reverse` the paper strips so the shiny side , is now facing the tape... I lightly press the paper strip back onto the tape...this provides a barrier between scalp-skin and tape ...it allows you to sit the system on, get it positioned properly and then you just remove the paper strips by using the creased-over bit as your grip -point.... you simply work your way around the edge, peeling the papers off and pressing the tape ` home` to /against your scalp..it`s fast and doesn`t delay the stylist.
If you`re ordering from separate suppliers, you`ll have no alternative but to make a 2nd template.