I haven't looked at any specific machines with this facility as I use TIG for this, but if you are going to have MIG but not TIG it is well worth considering a machine with a 'pull' spool in the gun, rather than just 'pushing' wire from the machine. This gives a much smoother feed as the liner gets a bit worn and it also makes it possible to weld aluminium. Thin aluminium is always more difficult to weld than steel so it isn't a good starting point - easiest to start by getting to grips with 3mm-6mm steel. However, once you have that working aluminium can be done, even down to LR panel thickness, using pure argon gas and a backing block to take the heat out. It is also much easier if you take parts off the vehicle so you can turn them around to make all welds downhand - with a backing block and downhand welding it is nearly impossible to burn big holes (someone will now prove me wrong...) You end up with more trimming off than you would with TIG so there is more work overall but it can give a perfectly satisfactory result - worth considering if you want the machine to be flexible.
The other option to consider, rather than MIG, would be a simple inverter type machine set up to switch torches between TIG for fine work and MMA (stick) for thicker section. It would cost you more in consumables for heavy section and it is slower across the mid-range thicknesses as it doesn't deposit as much metal. It would also give you two processes to learn rather than one. However, it would cover more bases overall once you got used to it and there is less to go wrong - it is generally the spool and feed which start causing problems on MIG machines, particularly the cheaper ones.
Alec
Edit: apologies if I have got the wrong end of the stick, but I have the impression from your door restoration thread that you have someone who you have been using for TIG welding previously. I am therefore presuming that you may not be overly familiar with using the various processes. If this is the case, it may be worth considering a short introductory course of evening classes (I know the colleges round here have got socially distanced courses back up and running). It would be an opportunity to try out techniques and equipment and see what you get on with; which features you like and which you never use. This could potentially leave you with a much better understanding of what you want out of a machine so you end up with something you get on with better.
