Problems with fillable PDFs

Question

I am trying to create a writable pdf and I took a cue from here: Creating fillable PDFs and What are the miminal required environments for a KOMA-Script scrlttr2?

I don't understand how to arrange things well so that it is easy and intuitive for those who have to use it. The code I am using is definitely not correct. would you have any suggestions?

\documentclass[%
  fontsize=11pt,
  parskip=half,%%
% fromalign=right,% right,locationright %% <============================
  firsthead=true, % <===================================================
  fromphone=on,%%
  fromfax=on,%%
  fromrule=aftername,%%
  fromemail=on,%%
  fromlogo=true,%%
  foldmarks=false,%%
  firstfoot=false,%%
  subject=titled,%%
  pagenumber=botright,%%
  headsepline=true, % <=================================================
  DIN
]{scrlttr2}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian,english]{babel}
\usepackage{url}
\usepackage{graphicx}
\usepackage{eurosym}
\usepackage{newcent}
\usepackage{lipsum}
\usepackage{selinput}
\usepackage{array}
\usepackage{hyperref}
\usepackage{xcolor}
\date{} %% elimina la data
\setkomafont{fromname}{\scshape \LARGE}
\setkomafont{backaddress}{\mdseries}
\makeatletter
@setplength{firstheadvpos}{7mm}
@setplength{firstfootvpos}{265mm}%%
\makeatother
\setkomavar{firsthead}{\raggedleft % <==================================
  \usekomavar{fromlogo}\[+1cm]
  \rule{\textwidth}{0.5pt}\
  \usekomavar{fromaddress}\
  \usekomavar{fromphone}\
  \usekomavar{fromfax}\
  \usekomavar{fromemail}\% <===========================================
}
\newdimen\longline
\longline=\textwidth\advance\longline-10cm
\def\LayoutTextField#1#2{#2} % override default in hyperref
\def\lbl#1{\hbox to 0.2cm{#1\strut}}%
\def\labelline#1#2{\lbl{#1}\vbox{\hbox{\TextField[name=#1,width=#2,bordercolor={white}, backgroundcolor={white}]{}}\kern1pt\hrule}}
\def\q#1{\hbox to \hsize{\labelline{#1}{\longline}}}
\def\qq#1{\hbox to \hsize{\labelline{#1}{\longlinee}}}
\begin{document}
%--------------------------------------
\setkomavar{fromaddress}{
    address\
    Street}
\setkomavar{fromphone}{Tel: +99,999,99,99,99}
\setkomavar{fromemail}{mail:email@blabla.com}
\setkomavar{backaddressseparator}{ - }
\setkomavar{fromlogo}{\includegraphics[scale=.5]{logos}\vspace{-1.3cm}}
\setkomavar{subject}{
money refund request}
%------------------------------------------------------------------
\begin{letter}{}
\opening{}
%\def\DefaultHeightofText{12pt}
%
\begin{Form} %%%%%??????
 Il/La Sig. \q nato/a \q il \q residente in \q Via \q, C.F:\q, in qualità di....
\end{Form}
\begin{Form}
 \mbox{\CheckBox[width=10pt,height=10pt,bordercolor=0 0 0,name=pri]{\ignorespaces}} {legal tutor} \par\
 \end{Form}
\begin{Form}
 \mbox{\CheckBox[width=10pt,height=10pt,bordercolor=0 0 0,name=sec]{\ignorespaces}} {family of reference} \par\
\end{Form}
\begin{Form}
\mbox{\CheckBox[width=10pt,height=10pt,bordercolor=0 0 0,name=ter]{\ignorespaces}} {The reimbursement of expenses will be made in the name of\q
resident in \q, CF:\q } \par\
\end{Form}
%  \opening{Dear Mr. xxxxx xxxxxxxxxx,}
% %
%  \lipsum[1-8]
% %
%  \closing{Regards,}
% \setkomavar*{enclseparator}{Enclosure(s)}
%
% \encl{example enclosure}
\end{letter}
\end{document}