Bending arrows in tikz-cd

Question

Following the advice of LaRiFaRi in an answer to this question, I switched from XY-Pic to tikz-cd. The file below contains my diagram in XY-Pic and in tikz-cd. Please help me to make my diagram in tikz-cd beautiful!

I would like:

1. To improve the problematic arrow from $\ell-1$ to 1;

2. To make the arrow tips sharper, as in XY-Pic;

3. To make the solid lines touch (or at least almost touch) the small circles.

Note that my diagram is an (affine) Dynkin diagram, so it should look as a Dynkin diagram, see these pictures.

EDIT: I took the corrected arrow from LaRiFaRi's answer and found suitable arrow tips in the library following his advice. Now the diagram is nicer than that of XY-Pic. Still I need solid lines coming closer to the small circles. Find below the corrected diagram.

 \documentclass[a4paper,12pt]{amsart}
\usepackage[all]{xy}
\usepackage{tikz-cd}
\usetikzlibrary{arrows.meta}

\def\ccc{{  \lower0.3ex\hbox{{\text{\Large$\circ$}}}}}
\newcommand{\bc}[1]{{\overset{#1}{\ccc}}}
\newcommand{\bcu}[1]{{\underset{#1}{\ccc}}}

\begin{document}
\[   \xymatrix@1@R=-5pt@C=10pt{
& \bc{0} \ar@{-}[rd]\ar@/^0.75pc/@{-->}[rrrr] &&  &&\bc{\ell-1}\ar@{-}[ld]
    \ar@{-->} `l[lld]  `[lldd]  [lllldd] \\
&&\bc{2}\ar@{-}[r] & \cdots  \ar@{-}[r] & \bc{\ell-2} \\
&\bc{1}\ar@{-}[ru] \ar@/_0.7pc/@{-->}[rrrr] & &  & &\bc{\ell}\ar@{-}[lu]
    \ar@{--2>} `d[l] `l[lllll] `[uu]  [lllluu] \\
}   \]
\bigskip

\[  \begin{tikzcd}[every arrow/.append style={dash},row sep=-5pt, column sep=10pt]
\bc{0} \arrow{dr} \arrow[thin,-{Stealth[open]}, dashed,bend left=20]{rrr} 
 & &[.8cm] & \bc{\ell-1}
 \arrow[thin,-{Stealth[open]}, dashed, rounded corners, 
        to path={ -- ([xshift=-1.795cm]\tikztostart.west) |- 
        (\tikztotarget)}]{llldd}
\\
& \bc{2} \arrow{r}[description]{\ldots} & \bc{\ell-2} \arrow{ur}\arrow{dr} &
\\
\bc{1}\arrow[thin,-{Stealth[open]}, dashed,bend right=20]{rrr}\arrow{ur} &
       & & \bc{\ell}
       \arrow[thin,-{Stealth[open]}, dashed, rounded corners, 
            to path={ -- ([yshift=-2ex]\tikztostart.south) -|
            ([xshift=-1.5ex]\tikztotarget.west) -- (\tikztotarget)}]{uulll}
\end{tikzcd}  \]
\end{document}   

Answer 1

You can try the dynkin-diagrams package. This example is included in the documentation. Note that by default, the affine root of this D series diagram is marked with a white circle, while the other roots have solid circles; you can easily change this if you don't like it.

\documentclass{amsart}
\usepackage{dynkin-diagrams}
\tikzset{big arrow/.style={
    -Stealth,line cap=round,line width=1mm,
    shorten <=1mm,shorten >=1mm}}
\newcommand\catholic[2]{\draw[big arrow,green!25!white] 
(root #1) to (root #2);}
\newcommand\protestant[2]{
\begin{scope}[transparency group, opacity=.25]
\draw[big arrow,orange] (root #1) to (root #2);
\end{scope}}
\begin{document}
\begin{dynkinDiagram}[edge length=1.2cm,
indefinite edge/.style={thick,loosely dotted},
labels*={0,1,2,3,\ell-3,\ell-2,\ell-1,\ell}]{D}[1]{}
\catholic{0}{6}\catholic{1}{7}
\protestant{7}{0}\protestant{6}{1}
\end{dynkinDiagram}
\end{document}

Answer 2

Maybe this?

% arara: pdflatex

\documentclass[a4paper,12pt]{amsart}
\usepackage{tikz-cd}

\begin{document}
\[
\begin{tikzcd}[row sep=-5pt, column sep=10pt,cells={nodes={draw, circle,font=\tiny, inner sep=2pt, minimum size=24pt}}]
     1 \arrow[dash]{dr} \arrow[dashed,bend left=25]{rrr} & &[.8cm] & 
     \ell-1 \arrow[dashed, rounded corners, to path={ -- ([xshift=-1.795cm]\tikztostart.west) |- (\tikztotarget)}]{llldd}
    \\
    & 2 \arrow[dash]{r}[description]{\ldots} & \ell-2 \arrow[dash]{ur}\arrow[dash]{dr} & 
    \\
    1 \arrow[dash]{ur} & & & 
    \ell \arrow[dashed,bend left=25]{lll} \arrow[dashed, rounded corners, to path={ -- ([yshift=-2ex]\tikztostart.south) -| ([xshift=-1.5ex]\tikztotarget.west) -- (\tikztotarget)}]{uulll}
\end{tikzcd}  
\]
\end{document}

I have not changed the arrow tips as the ones from xy are just ugly. If you want to change to some other style, just look into the manual. xy arrow heads are not included asaif.