It can make sense to focus on one or two types of claims. Each type of claim gives you the chance to go after a different category of infringer. A distributor or importer of a system may never take it out of the box and turn it on. They would not be liable for direct infringement of a method claim because they never performed the method. Think about who infringes a claim type. induces infringement
Without the full panoply of claim types you are not completely boxed in. You can cast a bigger net by suing over contributory infringement and/or inducing infringement as well as direct infringement. This might snare players where you do not really have the right claim type. Best is to be able to go after a deep pockets infringer who's infringement is very visible, for direct infringement.
Regarding the number of total claims - you only get three independent claims for "free". Each type of claim needs to be an independent claim. It is advisable to have more than one independent claim per type. If the applicant is a micro entity the cost for excess claims is not very high. $115 for each independent claim beyond 3 and $25 for each claim over the total of 20. It is possible that an examiner will restrict your application to only system claims or only method claims. If the restriction - that would get expensive.